I built a couple mild 4.7s and found the HO pistons to be a great and cheap upgrade. So are the HO cams up till 2007. They all just bolt right in like a glove. Port the heads a little, mill the block and heads for flatness and a tiny bit more compression... the 2008 up heads flow quite a bit more but have a big chamber and make low compression, maybe those pistons have a bigger dome.