Well, the differences seem to be with the center reflector only. The C4S has one, the others do not.
So.....here goes a lot of $ out of pocket just to see if this can be done.
I bought a used Ruf Duck Tail similar to this one shown on the Ruf web site that only fits the 996................
I will also buy a stock 996 C4S engine lid from salvage that I can use as a base.
A good friend who is an expert in fiberglass is going to make this Duck Tail fit the C4S lid.
When done I will post a photo of the results.
Len at Autosportengineering dot com