I missed the crash box info. You can swap the bellhousing for a 1948-53 unit and use either the truck 3 speed or a SM-420 4 speed to get some of the gears synchronized. Swapping the crossmember at the cowling for a 1954-up item and converting to an open driveline and a different rear axle will give you more options on transmissions, including the T-5 which is a fully synchronized overdrive 5 speed. Basically, everything from the bellhousing on back will probably have to be swapped- - - -nothing is a direct bolt-in fit.
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!