That's a really cool find. Do you have a clear image of the license plate frame? It could be the original dealer it was purchased from if it didn't come from a used car lot.
I can honestly say that the fuzzy image you have posted looks like it has a DANA Chevrolet license plate from on it. In fact I'd say I'm about 98% sure that's a DANA license plate frame. If that's true, you've got yourself a real gem. Of course without any of the original DANA paperwork or sales information, you're kind of out of luck making it really amount to any collector value. DANA sold new and used big block Camaros...along with other high performance Chevrolets. Too bad you don't know if it was ever a 427 conversion.
Here's a clear one:
https://www.yenko.net/attachments/56483-MVC-030S.JPG
Good luck,
Tony Huntimer
Camaro Performers Magazine