those heads dont flow very well, but i agree with the budge build idea. take the block to a machine shop that builds motors and see what they say they can do with the cylinder. maybe a hone and rering it with maybe new main bearings and cam bearings while you're there and its apart. just an idea. take your 5.3 heads and the mild cam you have run that combo until you save up some money for better heads/intake swap/cam swap should be a stoute DD and fun to drive/race.