For a 4 Speed?
I suggest you contact David Kee Toploaders to see what rebuild kit they offer. I used a kit from Marks Toploader Heaven in Oklahoma, but I am unsure if they are still active.
Those Marks site was good for the DIY job, but David Kee's site I am unsure of as I have not used it.
What to worry about?
- Detents and shift rails - they may feel OK on the bench, but years of forcing shifts and jamming gears can mushroom out detents, wear them out, or wear the shift rails. A perfect toploader should click-click into gears.
-Syncronizer bushings - they are the primary wear item on a toplader. They are the brass slip rings that aid in aligning gear speeds during shifts to avoid "grinding" between gears. You only know if these are bad by inspection, or by shifting the gears under a driving condition. When the syncronizers are bad, they often wear the engagement teeth on the main gear too.
-Input shaft Bearing! - The one that goes first and makes everything else wear faster.
The toplader sites have great information on this stuff and great pictures to show what looks correct and what does not. Most all of the parts are available, or you can have David Kee refurbish yours. They do sell all the replacement parts and offer a refurbish price of $350 plus parts.(I would expect the total to be close to $1000 on your average transmission)
I rebuilt mine using the kit from Marks Toploader Heaven. It came with all the syncros,gaskets and new bearings needed for a refurb, plus the specialty magnet tools and hand tools needed for re-assembly. Using the photos in his rebuild kit instructions I was able to identify worn gears and detents that I would have otherwise looked over. Mine shifts real easy on the floor, but I have yet to get it in the car and drive it.
Hope that helps. I suggest you get a kit and go through it while waiting on everything else, or open a dialogue with David Kee to have them do it.
kcmash