The 5.3 has different accessory locations than the 5.7L and might cause additional interferance. You'll have to come up with some motor mounts, cut the frame a bit for clearance, change driveshafts, etc....
There is a board member that emailed me a while back that was doiing this swap (5.3) but I don't know his board name. I'm sure he can add more.
You can also check out Street and Performance at
www.hotrodlane.com