If you're planning to keep the 3-speed, an upgrade to a Saginaw full-synchronized 3 speed will allow you to use 1st. as a traffic gear, instead of coming to a full stop every time you want to go to low gear. The Saginaw was used from the late 1960's on, and it will be necessary to fabricate a custom driveshaft because of the length, and the output shaft spline.
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!