[whitels1]

All the internal parts are the same size except the pistons are smaller in the 5.3, bore is 3.78 , and it's an iron block. You always have the option of boring the 5.3 block to 3.898 and using ls1 pistons to make it an iron block LS1. The ls1 heads do flow better than the 5.3 but LS1 heads can be found on craigslist all day for 100 bucks. Plus the truck accessories will be the way to go.