Comp cams xe268h for 318

BTW, I edited my last post with some more info/questions... we keep typing at the same time LOL

Those 273 rods should weigh the 726 grams. The rods you have in the '80's engine should weigh the 758 grams; that -645 PN looks right for the later, heavier rods. That is the one matter that may cause balance issues for using the early rods with the later crank. The heavier 273 pins should be able to be used to correct this but it is not a straight gram for gram change if the weight is added at the top end of the piston-rod assembly. Bobweight has to be computed for the original and new combination and the pin weight adjusted to make them match. The math is not hard!

Can you get access to a precise gram scale locally?

I think I see those pistons and rods on eBay. Look at the dish on the top of the piston; that is going to add something like 7 cc's + or - to the chamber volume and drop SCR and DCR by at least 0.5 points. Plus they are .040" over.... looks like non-starter to me.