There is another builder on talkbass - MPU in Finland I believe,that was also building multicoil pickups. I've seen some that were finished. I understand they were quite similar to Wal pickups in that they were 2 coils per string. Might be worth contacting him.
For what it's worth Ive had a Wal and an ACG. Both are fantastically flexible tone wise but still different. I loved both pre amps, but you definitely need to spend time learning how to get the sounds you are looking for.
I'm looking at replacing a bartolini humbucker currently in a warwick so will be following this with interest.