350 TBI to 5.3 ls1 1992 Chevy Blazer K1500

Hey guys! I have a 1992 blazer with a 350 and 700r4 tranny. She's ran like a champ ever since I got her. But she has 250000 miles on both the tranny and engine an I'm thinking about doing this swap for reliability's sake not to mention power and gas mileage improvements. I know Alot about these things, and have a buddy that knows even more that will help me. But I had to come to you all first. Whats yall's recommendation about the wiring harness? should i take them from the donor truck or buy a standalone? Pros/cons. Also the engine will be comming with a 4l60e tranny. Any tips pointers you have would be GREAT. Thanks guys :)

http://www.ls1truck.com/forums/lsx-t...zer-build.html

thats my build on same vehicle. only regrets were to upgrading to 35's and 4.88's, kinda cancelled any fuel savings. runs good though.