I think one of the most cloned Musclecars around has to be the 70-72 W-30 cars. Buyer beware, documentation is a must on these cars. I have seen numerous clones that are advertised as "numbers matching", but what some sellers mean is that the actual components match, but not to the car. Also beware any broker or "museum" that uses phrases like "442 with W-30 package", or "442 with W-30 option". Most knowledgeable dealers advertise these rare cars as "442 W-30", plain and simple.
Just got back from the Mecum auction, and saw a clone 72 W-30 convertible, created from a base Cutlass, sell for over $25,000. Quite insane considering the 350 4-barrel under the hood, but it sold.
There was also a numbers matching 70 W-30 4-speed, Sebring Yellow with black stripes. The car seemed complete, but had some serious body and paint related problems. From the audience, it probably looked like a 98 point car, but it really needed a lot of work.
On W-30's, aside from what was mentioned above by 442w30 up above, you have to see documentation, preferably the original owner paperwork, to verify these cars nowadays. Lucky for us Pontiac guys, we have PHS, so fake GTO's or Trans Am's are next to impossible to sell as real deals, unless an unsuspecting buyer believes everything the owner tells them, and chooses to go with their gut instinct. More often than not, you'll get burned.
By the way, Mecum was a hornet's nest for 69 Yenko clones. I was amazed at what some sold for, even poorly done ones.