Transmission tips

Hello everyone, just recently got my hands in a transmission to replace mine that’s missing 4th. I was wondering if there’s any tips for the job anyone has ? Anything I should be aware of before I try to put this one in (cleaning or prep of any kind?)

Also once I get my other one out I’d like to try my hand at rebuilding one, I’ve looked a bit for kits but I’m not sure how to know I’m getting the right one. If it helps mines a '97 sl