The 037 rally car I'm comparing Craig's S4 photo with, has wheels fitted, so it's hard to see the whole upright. What I can see of it, does look like a similar casting.

The chassis on the 037 doesn't look half as accomplished as the S4 one. Even down to little things like the anti droop cables. It's as if the 037 was a development hack for some elements of the S4? Obviously not the 4WD and turbo bit.