Unfortunately, the most likely culprit, the 2-3 synchronizer assembly, is scarce, and extremely expensive when you manage to find one. You're more likely to be able to find a complete transmission from someone who has removed the stovebolt six and column shift 3 speed and replaced them with a "belly button" ("Everybody's got one") small block V8.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!