How does the motor come back from the machine shop and you don't have the pistons yet? Aren't the cylinders machined to the requirements of the pistons? Do you have 902 or 906 heads? Not familiar with 902. What parts do you have, how fast do you want to run (don't know how fast your Chevelle is), and how much money do you have to spend. What's your car's weight, gear, trans... You want headers? That's a good price to power ratio addition if you can deal with the hassles.