I would lookup Dulcichs' iron head porting articles (Muscle Motors iirc). Good info. iirc said the 452's are a FAR better candidate for porting (if not cracked) but as said there's the OC issue to deal with but OC might be needed with quench domes if you want quench (as said wont be cheap) if you cannot get quench with flattops/dished and 915's. definitely unschroud the valves on the chamber ends. measure twice/check your budget/get estimates & go from there