yup, its only good to go the other way 4bbl mani 2bbl carb, and thats for special racing applications.... but yeah, those 2bbl heads are just going to cause you problems with a 4bbl setup..... if you want to do it, i reccomend buying a decent set of heads that are ported big enough for a 4bbl.... check out ebay.... sbc parts are a dime a dozen there