Standard shift, or automatic? The auto would be a cast-iron case Powerglide, with only two forward speeds. If it's a 3-speed stick, it's got a non-synchronized 1st. gear. If you're not interested in staying all-original, a turbo 350 3-speed auto, or a turbo 700 4-speed overdrive can be adapted with a minimum of fuss. If it's a standard shift, a Saginaw full-synchro 3-speed or one of the 4 or 5-speeds can be installed. How about some more details?
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!