I guarantee that when he takes out the clutch, the input shaft will wobble around. Clue is whine/grind in all but 4th, meaning trouble in case bearings and internal shaft alignment. I'd estimate about $700 to get the box professionally rebuilt around here, plus perhaps a cluster gear set (countershaft and all the counter gears is all one chunk of steel). Surface the flywheel and replace the pilot bearing is about another hundred or so. CenterForce dual friction clutch seems to be highly thought of here. No personal experience. I'm a slushbox guy.

I think you could rebuild the tranny yourself if you're handy. May have to get some things pressed, but I never did. Need a shop manual. Use 89 mitsu starion internal parts for all but the output shaft (if needed, not likely) as they are much tougher and address known weaknesses in a box as old as yours. I just sold a rebuilt 4x4 m/t to a pickup owner for $850....