The longblock is interchangable. Swap your oil pan, windage tray and pickup tube onto the 5.7L engine along with all your accessories and intake assembly and exhaust manifolds. You can convert over to the car intake, there is a writeup on the front page of this site on how to put an LS6 style intake onto a truck engine. Your only real concern will be tuning, you will need the tune in your truck updated for the 5.7L engine. You can also use the GTO injectors if they happen to be larger, you'll have to shim up the fuel rails a little for the longer injectors.