3 speed manual and 2.76 gears with /6

I drove a Dart Lite for years with the A833 OD and it was fine and dandy with the low rear gear and OD in the Appalacian mountains. I could cruise up all interstate grades in OD, even Christinasburg Mountain on I-81 and the WV Turnpike. On steeper grades I would drop it into 3rd and could climb any grade at 70-80 mph if I wanted. I do agree that you should look at your tire size and figure out how much % change there might be vs an A-body; some older low end 1/2 ton trucks came with 14" wheels and tires originally so you may be OK.