Brian, call this number 1-888-615-0780 and ask for Don. He usually picks up the phone. He has all kinds of internal engine parts at great prices. I've ordered many parts from him and have not had a problem yet.
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.
Thanks for the help guys. I'm gonna run out and get a set now. I don't think I will need anything super expensive. I plan on only using this engine for maybe a season or two. I'm going to stroke my 351C one of these winters. I'd hate to blow this engine up so I'm going to wrap it up and put it in "the vault"