the mk1 has a bigger engine bay than the mk1 and the chassis leggs are 2" higher on the shell so to put it in a mk1 you need to raise the engine by 2" and notch the chassis legs for the gear box and engine pulleys the rear beam bolts strait in and you can use the engine bed from the mk2 it just needs the mounts moving

as for the fous rs mk2 it has a wider track and the runningear is even wider than the st so you dont realy have a chance

my way would be make the engine and box fit get custom shafts but use a 2.3 volvo motor its cheeper and far stronger and use after market management