I did a 5.3 swap into my '69 Suburban, and it was pretty easy. I used
www.lt1swap.com for all the wiring harness modification info. I also sent my ECU to Brandan (lt1swap) to have him flash the theft and rear O2 sensors, plus configure the electric fan to come on from the ECU. It was very reasonable for price, and very quick turn around.
I took that motor out of the Burb and will be using it again in my '57...so that should let you know how pleased I was with it. However, this time it will get a pair of turbos and some other goodies.
Oh yeah, and when you get around to the fuel tank and whatnot, definitely use and in-tank pump. I used an inline external for quite some time and they are so noisy that you will be sorry you spent the money on it and will end up spending more to re-do it with an internal pump.