HevyHauler has the link for you, check out trannys with the O as in overdrive. Good chance it will be a Clark 5-speed. If it is a 264VO, 280VO etc...on the ID plate, grab it.
The best you can do is a .80 overdrive in fifth, but should bolt up to the 235/261 bellhousing with no mods.
I am going to look at a '59 dump with 261/5-speed also. Hope to find the big "O" as well. Good Luck!
1954 44001954 3800Jim D.
'41 Chevy 1-Ton Pickup/dump...292" 4-speed w/Ranger OD ... Newest Truck
'54 Chevy 3800 Dump........New Truck!
'54 Chevy 4400 flatbed/dump, Gone to my brother-in-law
'13 GMC 1500 daily driver ... 5.3 6-speed auto just turned 13k miles
'01 Chevy 2500hd, might be my new daily driver ... 6.0 / 4L80-E