NSU or small Corvair? It handles like a lemon blancmange. With some tweaking you might reach chocolate or raspberry, rather than progression to jelly status. Going fast is probably the last job to undertake on these things, especially as they are generally worn out. They are heavy, yet still highly malleable, as the steel is low quality. I am a great one for underdogs but I struggle to find very much good to say about these things.
As I say they would be very good at trialing with the low gearing, high ground clearance and appalling rearward weight distribution. Otherwise why bother uprating a car so inferior to a Wartburg, possibly even to a Trabbi.