main issue is you have to chop off the engine mount bracket on the driver side chassis leg, flip upside down then reweld it further back.
you'll need:
1. complete linkage inc stick, rocco stick isnt same as MK1 (bent) but i think it should fit? might be best to source a proper MK1 tintop or cabby 5 speed setup to be safe
2. steering rack
3. engine + box
4. complete fuel system, check the fuel lines they like to rot away.
5. check your fusebox vs the rocco one, if its the same engine loom will swap over, otherwise you need to replace the entire car loom. loom will work but some lengths differ plus connections to rear lights may not plug in, so biut o choppy n splicey, not hard tho, colours will match. dash clock plugs on a rocco are different but the clocks swap into mk1 dash with minor mods
6. check the fuel tank, if it has a lift pump you're laughing, it'll drop right into your old tank. if not you need to either source a mk1 tintop gti tank or find a lift pump setup off a later cabby/rocco
7. need the gearbox and driveshafts, easier to just swap the entire hubs across with shafts still attached. Plus then you also get the front brakes which will be worth having. Get the servo and MC too and if yours doesnt have the crossbar setup grab the lot!
8. rocco rear beam will have a roll bar, and it'll have a front one too. I'd swap all that over, you'll probably need the bones as well as they'll have holes for the roll bar, good excuse to redo all the bushes n balljoints.
think thats about it really