Gear ratio = [(engine RPM) x (tire diameter)] / [(MPH) x (336)]
2000 RPM at 60 with 32" tire needs a 2.72 final drive. Divide by the .70 overdrive of the 4R70W and you get a theroetical 3.88:1 final drive ratio. 2000 RPM is a little low to be pushing a barn door at 70. I would try for a 4:10 gear. With clean aerodynamics (mainly no lift and no big things hanging out in the breeze) and a good engine that is not hotrodded (may I recomend a bone stock 351) it should work well. Any upset (lift, performance cam, etc.) and it will be a dog. This will also limit you from ever going bigger in the tire department as well as you will already be at your ceiling. But get it right and it could be real sweet.
If you are not sure if a ratio will work right. Put it just in the rear and take it for a drive. Do not use 4WD while doing this, but in 2WD you can get a feel for it. Changine the gears in a 9" is about as easy as it gets. You could go through a couple of sets for fairly cheap before dropping the big bucks and setting the front up to match what you finally pick for the rear.
Ok my wives explorer with a 4r70w and A v6 at 70 is at 2000 rpm and getting 21 mpg I think the 302 would have more power than the v6 and I hope to get about 18 mpg I have changed build direction many times now
My 98 5.0 Exploder has 3.73 gears and 31 inch tires stock. 3.92 would be close to that final ratio with 32s. Seems to be a pretty good ratio on the road but probably optimized for a few MPH faster than you will probably drive the Bronco. That's with the Explorer 5.0 anyway. 4.11s would probably work well.
This thread is interesting. I'm lugging in OD at 70mph. 5.0-4R70W-NP205-31's setup with the stock 9" rear. I could change the rear gears and it would do better? Do I just buy the gears and swap em out? Donor?
I will counter that with my realtors Explorer. He went as far as a 4.30 gear and stock tire (he was still using it to take clients out) and the extra gear help it a lot and didn't really touch the gas mileage. It was down into the 15's on the track by the time he was done, full second faster then stock. The rear end finally ate a bearing and a stock geared Explorer rear end went back into it. I should have bought that truck...