Jan,
Re Wilksch. I thought they had a Wankel engine at one point in the '90s. I may be wrong.
Whoever it was had a single rotor demonstrator running in an ARV. The name Mistral somehow doesn't ring a bell.
Anyway, I'm maybe off topic because I don't think it was car derived.
I do remember the (made up) reg. being G-WANKEL. I suppose the correct number of letters would be inappropriate.
D.O.