I guess a lot of guys would pay that premium but not me. I would think that for it to bring extra $$$ it would have to be misrepresented. If I was going to do that I would just buy a motor with all the correct stampings that at least said it did once live in a chevelle. A CE block could have been placed in a variety of vehicles. It like the one I mentioned are still not the original motor. How do you describe it to someone after it is installed ...."This is a 69 factory replacemant motor that came out of another car. I do not know what model" After that it is only speculation.
A JA, JC, JD, JE, etc. coded motor tells you it was born in a 69 chevelle and the date gives approximation of build. Certainly a more original to a chevelle type motor and worth $5-600 unless it is a L-78.
But........As Always it is different strokes for different folks or egos in this hobby.
No offense just my .02.