I have been looking for an answer to this question with no luck at finding it so I thought I would try this forum. Does anybody know if 340 horse 409 stock heads will fit on a 348 with no modifications. I know the valves are bigger on the 340 horse 409 heads than most 348 heads and was just wondering if there is a clearance problem. I wanted to build a 348 stroker engine using the standard bore and wanted to used the 340 horse 409 heads to improve breathing. I am not interested in using aftermarket parts and I know the 425 horse 409 heads have too big of valves to use on a stock 348.