There was ofcourse also the 205 T16E2 of Philipe Wambergue. I think his one was stolen at a gasstation... I can remember reading (in Echappement?) something like that a that time... I about the same period the Gordon Spooner build roadgoing RS200 of Jan Langenberg was also stolen in Valkenswaard...
I think most of the S4's went to Autocross and one was not so long ago active in Bergrennen (hillclimbing). This was driven by Ianello and he beat Knutl in the specially build RS 200 with Godfrey engine several times...
I remember the S4 seem to have a very different wastegate noise...