[Scappoose]

Aside from codes, some things to check (and apologies if you know this) are that the 351 is actually a Windsor -- and actually a 351. I've seen Clevelands and 302s swapped in where people tried to pass them off as stock. Mach's all have 9-in rears, front disc brakes, larger radiator, and exhaust cutouts in the valance. If this is a finished car, the interior should be deluxe (woodgrain inserts, high back buckets, carpet with rubber inserts -- I believe red in all cases).

A GT trim option, I'm not sure. The GT is a different package. GTs and Machs have the same suspension. GTs usually came with the basic interior, though some did have the deluxe. Different stripes, wheels and gas cap on the GT.

Of course, sometimes the people selling aren't even sure what they have. I once looked at a numbers matching 69 Boss 302. What he meant was the numbers on the VIN tag matched the title and that it had a 302. He thought they were all Bosses. It wasn't even a 69, it was a 68.