what engine is it you have in the mk3? pretty much everything bay side will swap over except the rad, heater matrix fits as do the shocks from all 4 corners, wishbones, hubs etc. wiring loom plugs in if mk2 is 90spec, doesnt if its pre-90. but not always an issue depending what mk3 engine and what mk2 you want to put it into. fuel tank, pump, filter housign and lines also fit straight on, but may not be required again depending on mk3 engine ansd what mk2 you get to put it into.
manifold and downpipe will fit, get a cat bypass and it'll fit straight onto a mk2 16v exhaust system. isnt a lot from a mk3 mechanically that doesnt fit tbh, trim obv wont be any use.
rear seats pretty much straight swap, front seats fit using 90spec mk2 front seat bases from any model