I done this on mine a few weeks ago, abf box, depends which one you are using but as a rule of thumb, it has a hydro clutch and cable linkage, so all will need to be changed unless you use the 8v box, flywheel and clutch it will be ok. people say you need to change the pedal box if you go hydro, but ive had 4 mk3's and all have standard cable and hydro fittings on
apart from the obvious, you will also need to change the engine loom and ecu, the engine drops straight in, you will need the abf manifold and should be able to adapt it to your current system, thou the 8v's run a 50mm exhaust and the abf's run a 55 if I remember correctly
you will also need the ignition barrel, key and transponder to match the ecu unless you have an non immo ecu, apart from that, everything is plug and play, I ditched the aircon out of mine when I done the change, along with the abs and airbags. always have had to removed the master cylinder and once the brake booster
also you will need the according vac lines, fuel lines, hoses for rad, I think the rads are the same size. think its it really