How about 9R22.5, they are about 38" tall, that's what I will have on my truck, and what I had on a 61 f350. 0.80 OD, 3.73 gears, and 9R22.5 was just about right for the Detroit 6V53T in the Ford, I ran about 70 at 2900. 3.54 may have been better for fuel economy, as I was often traveling 75-85 while out west and empty, never over 2300 for long, fuel mileage was around 10 and truck weighed 10,000 empty.
I do believe you can hold a 5.9 at 2400-2600, but fuel economy won't be anything special.
Check out this forum:
http://www.4btswaps.com/forum/index.php Lots of good info on mostly the 3.9, much of it applies to the 5.9, and even some info just for the 5.9.
They should be able to advise on the proper engine speeds.
Another thing, I recently saw a new, or only a year or two old Super Duty 450 or 550 with the exact Rockwell axle I had under the ford, (mine from a 2004 Freightliner) an RS-15-120. it's rated at 12,000lb, excellent Hydraulic disc brakes and gears from 3.31 to 7.xx or perhaps slower.
Or, what about a new Chevy about 4500 size chassis, they have a nice 4 wheel drive setup with what looks like about a Dana 70 or 80 high pinion. I would imagine that gears could be had in the 3,xx or low 4.xx range? They have large 8 lug hub piloted wheels that are available in 19.5 or 22.5" (I ran the 22.5 wheels on my ford).
Grigg
