ideally you want to make the task as easy as possible. you wiil need

mk4 dash & clocks
mk4 wiring loom (saves cutting/joining wires)
mk4 indicator stalks and column/barrel
mk4 heater matrix and vent pipes.
the actual task is a straight swap the only probs are you will need to dril and tap two extra hols up the top of the dash(mk3 have 1 bolt hole/mk4 have 3!
Same as either side of the dash.
the most agro bit of the job is MOUNTING the air vent pipes properly as the mk3 mount completley different to the mk 4.
Then you will have the modern dask which does not crack and looks the mk4 (s2)dash is the only thing i prefer over the (S1) cars. Thats why my mk3 has the mk4 dash.you know it makes sense mate.DO IT