Did this on a mates MKJ2, doable in a day not particularly difficult. You need:
fusebox
clocks
stalks
ign lock housing and switch (old ign lock can be fitted to 90spec housing)
fusebox hanger
steering column outer tube
pretty much entire loom
header tank, or splice pre-90 plug to 90 loom
indicators, sidelights and horn looms have different plugs, swap or splice
lift pump, 90spec has 4 pins, pre-90 has 3. I think you might be able to disconnect the fuel pump loom near the round metal disc and keep the pre-90 loom section that runs outside of car?
FYI the tailgate loom can be disconnected either behind boot carpet or c pillar trim, so no need to drag it all out and swap