How long have you had it and did you acquire it in your area?
Learning where it sold new w/ an NCRS report could offer clues but try searching for any '72 Z28's geographically close, here's one guy in Lyndhurst to start...
http://www.nastyz28.com/forum/galler...php/photo/1042
Good luck!
[img]<<GRAEMLIN_URL>>/beers.gif[/img]
~ Pete