A bit more info... The heads show that they can be either:3998993....72-73...307/350......75cc chambers or
3998993....current..350.........Goodwrench crate motors,"Hecho en Mexico", 75cc chambers
Those are the head numbers.
The engine casting number is 3970010 which I think is either a 327 or 350. Could be 69 327 or 69-80 350...