Hey Jude. Good luck with the project. I just did a L83/8L90 swap in my '88 Suburban. Mine came from a 2015 Silverado. I love the engines, they run great and around me they are pretty cheap and are becoming more plentiful. I would stay away from the 8L90 transmissions. They are very buggy and I regret mine. I would recommend the 6L90, or get an adapter and do a traditional TH400. Also if you go the L83 route, do a full mechanical delete of the Displacement on Demand system. Just reprogramming the computer is not enough. The DOD lifters will blow up on you at some point so get rid of them.
The L83 is definitely a cool swap. I see traditional LS swaps all over the place around me but I have yet to see another L83 swap other than mine in a squarebody. I'm sure they are coming, but around me they still somewhat rare.
If you get time, take a look at this guy's youtube page:
https://www.youtube.com/@swaptimeusa
I'm pretty sure he is on these forums as well. He did my stock computer reprogram and I can't recommend him highly enough. He is the L83 whisperer.
If you decide to go that route let me know if you have any questions, I would be happy to help you.