[Mr70]

Welcome.
By chance have you located the original Buildsheet from under the backseat,carpet or door panels?
Do you have any Bill Allen Chevrolet specific documents for it as well?
It looks like it coulda been delivered from the factory to Bill Allen Chev.as a Super Sport,before being sent to DHPC where it was doctored down,(SS body emblems removed),to be a "sleeper" of sorts and have the 427cid.installed,among other items.
Do you remember if the tail panel was blacked out when you got it?
Good for you for obtaining it back.