I've seen a lot of strange engineswaps

[NoHachi]

I believe the older manta etc trannies bolt on to the C20. Plenty trannies available to hold more than 200hp. 4A-GTE is nowhere nere as reliable as a 4A-GE, so that argument doesn't hold in that situation.
C20's seem to be around quite a lot still. Though there does seem to be a difference in head design during some years that had the overheating problems you mentioned (You need the coscast head). The engine has had loads of testing on germany's circuits and loads of people have parts lying around. Buying a calibra turbo engine will always be cheaper then converting a 4A-GE and infinetly more reliable (always the case with OEM engines).

As for cost...if you know what you're doing it could be done for the about the same price as a 4A-GE. All the electrical stuff etc is just handywork.

@Zax. 200SX engine is just as good an alternative as any. Only the opel engines have a huge tuner support and knowhow here in Europe and I prefer NA engines to FI. But I'll admit that hunting parts down from a Japanese tuner has a certain charm when compaired with just ordering from a catalog from Helmuts tuning shop.

Basically: if you want to go fast NA and race the thing, then the C20 is a sensible option that might save you money. But there are always different elements that influence the decision and everyone in the end makes his or her own choice.
That doesn't mean that it isn't fun to argue about on a forum once in a while. Thats what its for right?