i bought a remanufactured engine from advanced auto parts a few years ago// mismatched heads one head rebuilt with everything new other head rebuilt using all used parts, 2 out of 8cylinders bored 80thousand the other 6 cyl bored 40thousand some new some old connecting rods same with pushrods and rocker arms a real mismosh of parts // but i will say it did run good but i just had no confidance in the long term life so i sold that car pretty quickly
you look at it if you're going to buy gm is all brand new stuff for really not all the much more money
by far the easiest way is a turnkey plug and play engine if you can strech the budget / i've gotten from
www.enginefactory.com and been very happy with the product