My first post on this site. I am restoring (I disassembled in 1987, yes-over 30 year project) a 1971 RS Z-28 but I am missing the original heads for the engine. My understanding is that I need casting numbers 3973487. The car has a build date 1st week of June 1971 and would like appropriately dated heads if possible. Does anyone know where I could get these heads either already rebuilt or re-buildable?