not to correct you, but to validate your statement....

yep - the door interior handles are different between mk3 and mk4.... I know because my mk3 cab has a drivers door from the mk4 pink ltd edition and the door handle didn't work properly... only when I stripped it down, and saw it was [pink, and therefore] from a mk4 that I realised the difference.

as for doorcards, my pink mk4 door seemed to perfectly hold the mk3 doorcard, although I can't confirm whether or not the opposite [mk4 doorcard in a mk3 door] would work....

I have seen a 90 spec interior fitted into a mk3 car but I'd have to say that I didn't have a close look, wasn't aware of any bodging that had been done to make it fit, and I wasn't sure whether the car still had mk3 or mk4 doors......

*** for anyone wondering why my cab had a pink door, I just want to point out that the pink door had been sprayed white and was impossible to differentiate as any different until I took the doorcard off [and saw the pink inside] and saw that the shape of the door mirror area was slightly different, as was the location of the interior door handle ***

how's that for a 1st post?