I've done some digging around on the internet and I think I know the answers, but I just want to double check since I haven't found the exact answers.

I've got an '84 MK 3 Cabrio project car with a 1.6 MFI engine in it that is leaking and sweating oil out of pretty much every gasket/seal. I've also got access to an '87 MK4 parts car with a 1.6 carb engine in it which in general looks in much better condition.
Could I just put all the MFI related parts on the carb engine and put that one in the MK3? The original plan was to rebuild the original engine but then I could still do that afterwards while still have a running car.
I know there's a difference between the older and newer heads (the MK3 engine has an 81SM6090 head and the MK4 one an 88SM6090), but since neither are EFI as far as I know it should be ok.

Apart from the MFI related parts, apparently the MK3 and MK4 engine mounts and gearbox housings aren't identical either. I assume I can just bolt the MK3 mounts and gearbox to the MK4 engine to fix that?

I've considered swapping to a Zetec or something else but decided I want to keep it more or less original.