Well done!
I think it's possible the whole roof might be from a Glas, as that front windscreen is from a Glas 1600 GT coupé.
I had it as a VW special, so I think that's probably what powers it, as it certainly appears to be rear-engined.
I think I'll give you a point and call it solved as we are probably unlikely to get more information, but if anyone does know more there's always the possibility of another point!