How willing are you to do the work?
1.6NA engine needs a switched live feed to operate the fuel solenoid. Thats it!
Of course there is temperature sender (should be the same) maybe oil if you got it and the gti rev counter wont work. Theres also glow plugs, but thats something you can add in the engine bay. You'd need the glow plug relay which is a timed relay, some wire, a light for the dash and thats about it. The relay has 2 large terminals, in from a 50amp fused supply, out to the glow plugs its got 4 other connections ( I think from memory) T - which is a temperature switch on the end of the head, L - for the lamp on the dash, a ground and 50 - this is the connection on the starter from the ignition that makes it start.
I'm sure thats pretty much it.
Its far easier putting a diesel in a gas car of this age as no complicated electronics and mostly about 6 wires.