What exactly have you done; what parts did you replace, did you remove the shifter shaft, replace the bushings, coupler, striker plate, adjust everything correctly, etc. and what inspections have you done?
After almost 50 years of use, parts will be worn out and in some cases just fall apart.
With the trans axle removed, did you remove the nose cone; inspect the shifter lever for wear or damage? I lost all my gears and found the lever to be broken off.
Like any problem, its about narrowing down the problem; until you find the cause of the issue, a process of elimination.
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