Put it on mobile.de. It will sell fast, even with a decent price tag. I don't think I've ever seen another one in white with white tombstones, sunrooof, rear wiper and pop outs. The German market is the place to advertise it.
Quite a chunk of difference between a Carrera 3 and an early SC - the C3 certainly honours the Carrera badge. I've run mine in anger against a 235bhp '75 euro Carrera and it had no trouble - 200bhp underpinned by that lovely 6 bolt crank which loves to rev and mine is fairly light.
The 964 will be a bit less maintenance and probably a better regular driver, C3s are not a car you can lock up and forget for 6 months at a time. You should get a proper C3 badge on that tail if you are going to sell it - it will make a difference.