No statebound S30's got an O2.
5/16".
Its not just the injector ports... the bolt pattern is different.
Loosely speaking, you could say that about any EFI system
This '78 EFI schematic may help, Alsil...
One thing to note is that it uses an oil pressure switch for the fuel pump. '75 and '76 used a switch integral to the AFM, '77 and '78 use a specific oil pressure switch.
If you're truly looking for "Barebones", in most cases, you can delete the cold start valve, thermo-time, and altitude switch.... and if you're really bent, the air regulator can go as well (fast idle).
As I mentioned in your crosspost, you'd probably be better off with a Maxima system.