Hi Steve,
the comprehensive answer is in the B.K.P. shop under 'accessories' I believe. Meanwhile I had my Stormy Mondays changed from AII to AIV a few months back, and I seem to remember it being a very reasonable £10 per pickup ( which included re-potting e.t.c ) . B.K.P recommend a recorded delivery service to them, and charge for a recorded delivery service back to you. They also do 'add ons' like new external wires, 4 conductor to 2 conversions - and of course the complete ' vintage rewinds' for those odd shaped pickups that you want converting to B.K.Ps.
As always, they provide great workmanship and returned mine very quickly. :D