The piece was then trimmed to the right length, the corners were rounded, and the top was shaped with hand tools until it resembled the other pickup, as closely as possible.  After a light sand to about 320 grit, the cover was put aside while I turned my attention to the coil itself.

The vulcanised fibreboard which was used for the top and bottom of the bobbin was reheated then flattened in a vice.  Then the whole thing was reassembled making sure that the magnets were all polarised in the same direction.  After checking the magnetic polarity of the other pickup, I selected the "down" side of the bobbin and installed a PCB pin so that it would eventually protrude from the epoxy to allow the start of the coil to be soldered to the pickup lead.  Its important in these situations with two single coil pickups, to have one showing North and the other showing South, when a compass is pointed at the top of each pickup.  This way they will hum cancel (to a certain extent), when both are turned up.  After testing the DC resistance of the Riverhead pickup, I rewound my reassembled bobbin to the same reading using my hand cranked pickup winder.  Following this I installed another PCB pin and soldered the end of the coil to it.

The inside of the cover was then lined with copper shielding tape, while the outside was stained black.  I also let a small square section of the copper tape come over the side of the coil route to be used as a solder pad for the shield of the pickup lead.

The cover was then half filled with runny clear epoxy, and after the coil was gently pushed into place, I topped it up with more epoxy, being careful to leave the solder pins just peaking out. The epoxy to use here is the slow curing type.  This allows good penetration into the windings and also allows any bubbles to escape.
Recently a mate of mine brought over a funky little headless Riverhead bass that he'd picked up up at a second hand shop.  He asked me to remove the pickups and dismantle the hardware.  His plan was to have the metal parts replated, while a panelbeater friend of his resprayed the instrument.  While playing it, though, I noticed that the back (bridge) pickup wasn't working.  After some testing, just to make sure it wasn't a dodgy pot or pickup lead, I removed it only to find that the pickup coils were potted in epoxy.  This, and the fact that we had no luck finding a suitable replacement, or in fact any commercial pickup of similar size, made things a little complicated.  My mate gave me the green light to try whatever I could, so I decided to have a go at removing the potting, and rewinding the bobbin. 
Many epoxys will start to soften when heated to a certain point.  Of course I had no idea what that point was, and more importantly, if it was a lower temperature than the softening point of the plastic cover!  I hoped it wasn't, because it would mean I could reuse it.  The temperature guage was useless here because, I ended up having to crank the hotplate to the point where the water was really boiling.

After it was submerged for maybe 15 or 20 minutes, the black epoxy just softened to about the feel of hard rubber.  I was able to gradually cut around the edge of the pickup with a razor sharp hobby knife.  I had to keep returning the pickup to the water, because the epoxy would harden again after only a minute or so.  Eventually I had made a cut deep enough to get at the bobbin but as you can see, the upper piece of the bobbin remained in the cover.  After a couple more spells in the heat and a bit more surgery, I was able to remove it but I noticed the sides of the cover just starting to deform slightly.  I hoped to tidy up the job by removing  just a little more epoxy from around the edges of the hole, but without the support of the bobbin, the cover buckled badly when it hit the water for that last time.  This was very disapointing, but if I had to do it again,  I don't think it would happen the second time.  Without the pickup lead to hold (after most of the bobbin was removed), I was rellying on an old pair of kitchen tongs.  Worrying about crushing the softened plastic of the cover, I had allowed it to get away from me and go too close to the bottom of the saucepan.  Next time I'll place a mesh platform of some sort in the bottom of the pan to rest the work on.
I now had no choice but to construct a replacement cover.  For the job, I chose a scrap of Budgeroo which is a very fine grained Australian timber that is not particularly hard, and consequently machines very cleanly.  After trimming to the appropriate width and height, I used the other pickup as a template for the holes.  It was clamped directly over the work in the protected jaws of my drill press vise.  Then I removed the Riverhead pickup and countersunk these holes with an oversized drill to match the width and depth of the countersinks in the original.
Next, the recess for the coil was routed.  I used the fence on my router table and progressed cautiously in small increments until the thickness of the top was about 2mm.  The trick here was to get it nice and thin so that the pickup had a similar response as its partner in the neck position, without needing to be adjusted too much higher.  On the other hand, if I hadn't planned on re-potting the pickup, and was simply using foam rubber to hold the coil up to the cover, I might have made the top a little thicker and therefore more durable.
The piece was then trimmed to the right length, the corners were rounded, and the top was shaped with hand tools until it resembled the other pickup, as closely as possible.  After a light sand to about 320 grit, the cover was put aside while I turned my attention to the coil itself.

The vulcanised fibreboard which was used for the top and bottom of the bobbin was reheated then flattened in a vice.  Then the whole thing was reassembled making sure that the magnets were all polarised in the same direction.  After checking the magnetic polarity of the other pickup, I selected the "down" side of the bobbin and installed a PCB pin so that it would eventually protrude from the epoxy to allow the start of the coil to be soldered to the pickup lead.  Its important in these situations with two single coil pickups, to have one showing North and the other showing South, when a compass is pointed at the top of each pickup.  This way they will hum cancel (to a certain extent), when both are turned up.  After testing the DC resistance of the Riverhead pickup, I rewound my reassembled bobbin to the same reading using my hand cranked pickup winder.  Following this I installed another PCB pin and soldered the end of the coil to it.

The inside of the cover was then lined with copper shielding tape, while the outside was stained black.  I also let a small square section of the copper tape come over the side of the coil route to be used as a solder pad for the shield of the pickup lead.

The cover was then half filled with runny clear epoxy, and after the coil was gently pushed into place, I topped it up with more epoxy, being careful to leave the solder pins just peaking out. The epoxy to use here is the slow curing type.  This allows good penetration into the windings and also allows any bubbles to escape.
The following day, I sprayed the pickup with a good wet coat of polyurathane that was furthur blackened with a little powdered pigment.  This stuff also dries slowly,  (not like nitro lacquer), but I wanted the extra durability of this finish.  After two more coats (a day apart), I let it cure out for a few days, then gave it a polish and soldered a piece of twin-core shielded wire to the pins and the copper pad.  This way I would be able to reverse the phase of the pickup while retaining the earth potential at the shield if I needed to, without removing it again.  It also would allow me to wire the bass with a single volume control, and a series/parralel switch as requested by the owner.  (He said he would like to used the bass with both pickups turned right up, and initially wanted them both hard wired to the same volume control.  I suggested the switch as a way of filling the spare hole and having an extra tonal option that still cancels hum.)

The lowest image on the left, shows the bass with its chrome hardware, funky paint job, and "new" bridge pickup.
Custom Riverhead Pickup
Custom Riverhead Pickup