Agreed. Roof and B-pillar areas can be a concern on these cars due to the quick-and-dirty way the conversion was done.
I doubt many clones of them are being done because they're not a high-dollar car, but always check build date on the body plate (should be 04 or 05, April or May) and check the DOT markings on the quarter glass. If they are visible about midway down the lower edge of the glass, odds are good it's real. If you cannot see them, car has had quarter glass replaced or is bogus.
Also- they were available with 350 engines, so if VIN has K or M engine code and all other Hurst clues check out, not a problem. You will find the 350 engine cars are generally not as optioned out as the W30 455 cars. Most of the 350 cars also had 14" Rally III wheels with bolt-on center caps, whereas the 455 cars had 15".
Mopar guy on hearing my Hurst/Olds thru Flowmasters.. "TURN THAT DAMN LOUDASS OLDSMOBILE OFF!!"