My $0.02 - I think they are possibly different cars, and the craigslist seller just "borrowed" a photograph from the Mecum auction of a car that looked just like his.
If they are the same car, at a minimum, the big block has been pulled out and a small block put in place, and the front and rear bumpers have been changed (the ones at Mecum didn't have bumperettes, the one in the Craigslist ad does, and even in the first picture on the Craigslist ad (which is the borrowed one), the front bumperttes are missing.)
Edit: The exhaust where it comes out under the bumper looks different to me as well - the one in the Craiglist ad has what looks like clamp bolts hanging down where the tips are bolted on, the one from Mecum looks to have resonaters and welded tips and tucked up tighter and not sticking as far out from the bumper.)
Or, as the OP said - there is some sort of real scam going on here...