this is a great forum and im very happy to be here and I know I will find many things about oldsmobile and other related info in the classic car world,as I just got myself a 1968 455 396021F with "C" heads motor the I want to drop into my 1971 LeMans. and right now im just going over the motor to see if it realy is a 68 or 69-70-71-72 lol. I know it's not a Fa block and the pad under #1 cyl where the casting # is to smooth to tell thanks to me using to much force with the wire wheel,i hate my self for that one and sure the oil filler starts with a 8 for the stamped casting# but that could be replaced.there a threaded hole at the rear drivrs side of the motor near the frost plug or starter bolts and im told the Fa motor does not have that 3/8 hole . so its 68-72 but which I wont say for sure. I know there are some olds wizards on here so I things are be looking up.

 

That number is a VIN derivative, not a casting number, and it's the only way to tell for sure what year the block is. The real question is, who cares? The C heads are 68-69 and could be either big or small valve. The oil fill tube is 1968. The intake, heads, crank, block, pistons, and most cams are the same for the two years. The biggest difference from 68 to 69 is the A-body exhaust manifolds.

 

For more help with that Lemans, may I suggest ForeverPontiac.com

As for the motor, the ground away number may be legible if you rub it with a graphite pencil. I've had good luck with that. Alternately, a mild acid may bring it up.