Well, I will be selling my 400 soon, and I want to know for sure if it has ever been rebuilt. I'm pretty sure it hasn't, but I'd like to be positive. Everything on the motor is original, and I even still have the original GM oil pump, which I replaced summer 2002. The pistons have GM and a number cast into the skirts, so I know theyre not aftermarket pistons. Also, there is no oversize number stamped into the piston tops. Would it be possible for someone to just put oversize rings in it? Is there a good way to measure the cylinder bore? Lastly, how much would you guys say a standard bore 400 is worth, with the original 882 heads?

 

gm bearings, aftermarket gaskets, plastic cam gear would all be clues. measure the bore with a bore gauge, or snap gage and mic. i'd say 400-500 dollars is a good price, really depends on what someone is willing to pay.