[factorystock]

Any truck trans that wasn't originally installed in a pickup will need some modifications ( drive shaft shortening and parking brake drum removed possible trans hump enlarging ) to make it work, but the 3153 was optional in Chevy medium duty truck during this era, doesn't show 3151B. If it is indeed an overdrive unit like the 3153, it would be a nice upgrade. .8 overdrive works better for working trucks compared to the .7 overdrive found in most all modern pickup overdrive transmissions. Since the '66 transfer case does not mount directly to the trans, it should work with minor modifications.