Excaliber,
As you say, this car may not be a good market value test for a Chevy powered cobra if it goes high teens or breaks into the 20's.
On the other hand it may be a decent example. You see, the buyer of a low priced cobra may not be the same type of Cobra conniseur as is the buyer of a $40000 Cobra. They may simply want a pretty car and for <$20000, you find those folks.
Ive seen a couple of FFRs (no offense to FFRs in general intended - these are specific examples) that were; how shall I say it? "less than refined" in appearance, but had Ford power (still a late model, stock, FI 302 is not really any more correct than a chevy in my opinion, but that has already been argued ad nauseum). Maybe I'm crazy, but I think if you parked my car (not perfect, but a pretty nice, finished, car) next to a low-buck Ford-powered replica and asked most passers-by, which car they would buy, given they are the same price, I think most would go for the nicer car, irrespective of engine make.
The reason I think this comparison may be valid is because the <$20000 buyer is closer to the general public than a Cobra conniseur.
I suspect that as the price line lowers, the spread between Chevy vs Ford powered decreases. A Kirkham, well done with a Chevy will be way less than one with a 427 Ford (likely $30000 difference or more?). A $15000 car with a Ford motor doesn't have $30000 to take from its value if it were to have a Chevy motor.
Just some thoughts to stir the pot, since my earlier post to this thread didn't return me any threats...