The only "must do" thing when swapping to a big cap HEI is to be sure that the oil pump drive tang engages fully into the pump lugs. Compare the distance from the vacuum advance bracket on the original distributor to the end of the shaft tang, and do whatever is necessary to assure the length of the replacement matches. Just for insurance purposes, I usually machine the flange off the HEI and fabricate a bracket that can slide up and down the housing to assure I've got full engagement of the pump drive. The part of the old vacuum advance bracket with the pinch bolt works well once the vacuum chamber is removed, or you can fab one from a piece of 3/8" X 1 1/2" aluminum flat bar with a slot and a pinch bolt.
Jerry
