/6 questions

I think the AX15 or NV3550 might be a little on the fragile side for what's probably going to be a 6000 plus pound vehicle. However, on the upper end of the scale, there are tremec TKO kits for AMC. If you could find a bellhousing adapter an NV3500 out of a two wheel drive V8 Dakota would be optimum, look at this ratio set.
Close Ratio NV3500-HD Dodge Dakota Gearing:[6]

1 2 3 4 5 R
3.49 2.14 1.38 1.00 0.73 3.55
With a 7.17:1 axle,
25.02 1st, 15.35 2nd, 9.9 3rd, 5.23 5th, and 25.45 R. You had mentioned 20 inch rims from and international axle in one of our messages, I am guessing 10 lug?