Hi Roman,
You do some quite impressive and detailed work! Really like it.
Because you modify de body in such a detailed way, I just had to point something out. On the original Sport quattro rally cars, the front grille with headlights was similar to the one on the street versions. Some have small closed rectangle areas in the lower corners and some haven't.
The headlights should therefore be bigger and less square. On your model, they are really square.
The car you posted pictures of has the grille of the S1, so not original for the Sport quattro.
Here are some pictures to illustrate that:
Street version:
Original rally version:
"Your" version (I think it's the 1985 hillclimb version):
S1:
I hope it's a bit clear what I mean with this... If I spoiled the thread with these pics, please tell me and I will take them down.
good luck with your awesome work!!