Suspension, not just coily kits maybe uprated springs and shock seperately and as kits too?
All the adjustable bollocks that you lot do for the S bodies would be nice, cambers castors, locks blah blah blah.
Adjustable and/or uprated ARBs.
Defo a well developed bucket seat mount which would fit a seat low and in the correct position (hard to do in a e36 at least with universal stuff due to tunnel and offset steering/pedal position)
Poly bushes sell well for BM's as BM's, especially big ones, cane bushes.