You could build a cartridge holder from PVC per this site-
http://motoman393.thumpertalk.com/tech.html
I've made one up, and it works well (and it's real cheap).
Some just use an air wrench to spin the base valve out, so they have no need for the cartridge holder.
As for replacing fork seals, next time I'll spend a few bucks for a genuine fork seal driver, because it's tough to find an exact match with PVC.
I haven't played with shims yet, so I have no useful information regarding that. ;)