that'll be k-jet then, if you kept the existing system a mk3 lump would go in mostly without modifications, just need to buy a dizzy adaptor gear from TSR so you can fit your old dizzy, plus swap the dizzy gear from the MK3 dizzy onto it.
with the 16v you could keep the k-jet system and run it on kr managment, but since most of the 8v stuff will need to be stripped out and replaced with 16v stuff anyway you may as well run it on the proper abf mangment.
with either the 8v or 16v, running it on the MK3 managment is an option if you can handle a bit of wiring, theres not really much to it tbh. main thing is you want a lambda probe fitting in your exhaust to get the best out of it.
I have various wiring diagrams etc to help you here, or alternatively if you supply your old engine loom + the MK3 loom I can make you one.