If you think the engine ran ok before wait till you replace the timing set...Id venture to say that's stock, last time I saw a nylon tooth timing gear was in a 69 Coronet 500 I owned that had a 318. This was way back in like 1990, around when they all should have been replaced LOL!
I think your right Dartswinger70, I checked the bore and it is standard so I don't think the engine has ever been rebuilt. The original owner is still alive and I have been meaning to ask her where they got this 318.
