Mainly speaking from an injection point of view.

The holes for the K-jet injectors on the E21 head look like they would fit an E30 injector. I haven't actually tried to fit an EFI injector in there though.

Does anyone know if the casting for the injector holes are the same on both the E21 and E30 head???

Thanks,
Windy

in the 323i there different between k-jet and efi..hatter knows for shizzle
i think u can get bungs or can open them up a little to fit. can't remember if the k-jet is bigger or smaller

Kjet is smaller than Motronic.