if it is a 427 block, hp wise stock will not matter if you rebuild it and put in upgraded parts. the early ford blocks were all very stout and can take a severe build. but if the guy will not let you properly identify the block, you might want to cut and run. there are still a alot of 429/460 cores available everywhere and parts might be a little easier to come across then the 427 anyway. I would not buy a motor if I did not know what it was!