Possibly I can help. Hi-po's used standard Mustang pushrods that came through a slot, not a hole, in the HP head. The slot served as a guide. These were standard Mustang pushrods that were 6.825" long; with part number C2OZ-6565-B. There is however, at least one Ford parts manual that lists pushrods as "hardened." Strangely, there are others that do not. Moral of the story is, buy a hardened aftermarket 289 pushrod that is the correect length and you won't have any problems. Good luck.