Okay there's a lot of variables in your question.
1. WHY? Rebuild your 4l60e.
2. If you must swap back in time to a 700r4, there's only 2 problems to the best of my knowledge:
- Need the kickdown cable, and must attach it to the Throttle Linkage of the TBI system.
- If you want to lockdown the torque converter, you must make a switch. There's aftermarket ways to do this via a pigtail wiring harness, or im sure you can build your own. Im not sure what would happen without the lockup.
3. What are your plans anyways? I'd keep the stock wiring intact, build up a 4l60e or 4l80e and stuff it back in like there was originally.
4. If your stupid enough to downgrade to a 700r4, just yard everything out if you want, i don't care. lol
WAIT WAIT WAIT
You have a Vortec 5.7? Your going to have to custom mount a linkage on the throttle body. Good luck with that.
Furthermore, just or safety sake, your going to have to delete some parameters in the ecu. I have no clue how the Vortec 5.7's are reprogrammed. I dunno if EFI Live/HPTuners etc. even supports that engine platform or not.