As said, shape wise they are the same, colour was also different tho

Mk3 only had clear or bronze tint, mk4 only had clear or green, (mk5+6 had clear or green aswell)

So if you want it to match you need to work out what tint you have (best, hold a sheet of plain white paper behind glass and look fron outside) and get a matching one - so a mk4 screen will only match if your cab is clear and the mk4 clear also (unlikely, most cabs had bronze)