3 speed manual and 2.76 gears with /6

Just wondering if there was a a combo like this. 3 speed manual and 2.76 gears with /6. Im asking because I'm thinking of this combo with my 64 Utiline D100. No towing or hauling only driving.

I have had many d-100's all of them had 3.55 or 3.91 stock.

What you have proposed with 2.76 gears will not work, think of it you are shoving alot of frontal area in the wind, most likely with 28" tires.
With that combo you will not be able to hold 70mph up hill on the interstate.

The truck is not an A-body that has somewhat aerodynamics, it is a big flat brick.