you can use all the electrics from the car, a chip may help but the MAF sensor should cope ok.

to get the engine in tho you need to change:

Water pump (might as well do cam belt and tensioners while your at it)

Im pretty sure the mondy oil pump is ok, but the oil filter pokes a bit further out

you need to change over the oil pickup pipe and the sump

you need to change the flywheels and clutch over unless your GTI has an MTX75 gearbox (will have a lift reverse if so, if its normal ford bottom right reverse its an IB5 box)

and thats it