It all depends on what you have now. Guys have switched out 4.8L long blocks with the 5.7s and been really surprised. The engines are basically/dimensionally the same. Intakes to oil pans interchange. You can pull all your accessories and bolt them on the LS1, except one bolt hole on the a/c mount is what I hear. The headers will be the same from any of the LSx heads. The LS6 and H.O. 6.0L engine both have D shaped exhaust ports and the rest are round. They all use the same headers since the bolt patterns are the same.

What are you running in your truck? Year model?