if you bolted a MK1/2 020 box to it (i.e. your old one if it shifts ok!) then it will drop in using all the original mounts, gear linkages etc. Just get yourself a new sachs clutch kit and bnolt on your old flywheel. Easy swap.
Next problem is the exhaust system, as I say 4 branches for MK1 16v are available off the shelf, but ideally you want to find some people who have abfed a MK1 to find out what work and what dont, the issue with ABF is it a bit taller than a KR lump so sometimes there can be clearance issues depending on the make of 4 branch. Good news is on a MK1 you can change the manifold/downpipe with the engine fitted, as unlike a MK2 it comes out underneath the steering rack and there is no subframe in the way
Once you get that sorted, if you go with the ABF managment you need to get a lambda probe boss fitted to the 4 branch, if one is not already fitted, as I say you can whipo the 4 branch out once the fitment is all finalised, or it can be done in situ, my mate james had a boss fitted by the phirm after the car was together & running no problem.
Last hurdle is the wiring. A bit of wire splicing and loom tweakage will be required as a) the MK3 has the fusebox on the opposite side to the MK1, and b) the fusebox plugs are different. What I do is to remove the engine loom (leave the lighting loom alone) and strip off the loom wrap. Every 20cm or so, wrap the loom with tape so it keeps its shape roughly, then remove everything that isnt engine managment related except the black and red/black wires to the coil. Leave the wires for the coolant temp, radiator etc, just remove things like the carb heater wires, that kind o thing. Keep the coil, dizzy & TCI-H loom handy, as you need some of this later.
Now get your ABF loom and do the same thing but remove everything that is NOT engine related!
What you want to do is keep as many of the MK1 wires as you can, to reduce the splicing required later. Also bits n bobs in the MK3 bay have different plugs on, plus the lengths are all to pot. What you should be left with is a pretty much standalone ABF engine loom, with only a very small number of wires to the fusebox left
Last thing to do is to cut off the MK3 coil plug, bin off the black and the brown wire. You should be left with the signal wire from the ECU. This wire needs to be spliced to the wire attached to pin 6 of the TCI-H unit, this is one of the wires to the MK1 distributor. Once this is done the MK1 dizzy plug and the other 2 wires can be binned, you only need to keep the ones that connect to the coil anbd the battery -ve. This ensures that your MK1 rev counter will work right out of the box, plus you also do away with the rubbish MK3 coil.
Once you get to this stage, you need to combine the 2 looms together, and push the MK3 loom thru the MK1 bulkgead wiring bung grommet thing. Once at this stage you need to trial fit the loom, and decide what needs to be done to get the lengths right. Handily most of the ABF loom is attached to a big round plug on the front of the engine, so you'll probably find the loom just needs to be shortened a great deal to reach the MK1 fusebox.
Then its just a case of i/d the wires on the ABF loom, and figure out where to splice to. My fusebox FAQ should help here
It all sounds pretty complicated, but its easier to do it than it is to explain
I'm at the last stage on my MK1 kr conversion, I have a MK1 bay loom, MK2 ISV loom and a corrado ign controller loom to combine together
