I’m stroking both of mine 4.15 x 4.31 iron head in the 66 Belvedere and 4.5 x 4.56 aluminum head in the 64 Savoy, both with 12.5 pistons. If I have to put 15 gallons of race fuel in them to go to the Queen so what, a dang meal for the wife and I is an easy $50 now and the smell of race gas is so sweet.