4 speed ka-booom !

Hard to see from pic's, but that trans look's good from here, buy the rebuild kit from Wayne at Brewers, and reassemble the tran's. Oh, just out of curiosity did you check the splines on the main shaft? If there good I'm thinking your barking up the wrong tree. Get an interior snap ring pliers, and dissasemble that main shaft, take pic's so you have a good reference when putting it back together. If you have any questions just shoot me a message, there not very complicated.
Jeff