Overdrive Swap Economics

[BigBlocksRule]

Doing something similar on my '85 with a 454.
$305 gets you a new TBI wiring harness set up for the 4L80E. Computers are cheap, so are TBI units and adapters. I have a 70K mile 4L80E that came from a wrecked truck, I paid $250 for it, changed fluid and filter and I'm going to run it as-is. The one in my current work truck has 235K with nothing more than occasional fluid/filter changes. Add a cooler if you're going to tow and that's about it. Mine is a dual tank truck, I scavenged the switch, tanks, etc. off of a parted out truck so I can use 'em both.
Don't make it more complicated than it already is!!!