A build sheet is the only REAL way
Other clues:
VIN starts with 34467, 77 or 87
VIN 7th character is "M"
Red inner fender wells
Posi
disc brakes
Muncie 4 speed or TH-400 with "OW" tag
OAI hood and air cleaner
boxed rear control arms and sway bar
fender braces
F-block 455 (don't forget to check for numbers matching)
W-30 aluminum intake
ANYTHING can be cloned. And Olds doesn't have anything like Pontiac's historical documentation services. You don't say where you are from,but check
www.oldsclub.org and see if there is an OCA chapter near you. I'm sure there would be a pro willing to check it out for you....for a fee, of course, but at least you could be "more" sure.
Caveat emptor and all that.
C.J.