The Allison 1000 and 2000 series are about the same size, length and diameter. The 3700 is about 20" larger and bigger around. Is it possible to connect a 3700 to a 5.9? Does the 5.0 have enough power to turn a 3700?
not sure why you would run it? I guess 7 gears is nice if you do a lot ofhill climbing and want to downshift alot. and allison 2500 school bus transmission is 6 and 6th gear gives you a better overdrive..
a 3700 series is likely going to be expensive to obtain and then you need a converter and adapter ring for your engine.. I dont know if the 5.9 was natively and sae2 or not.. I think a #2 flywheel housing is available. for the cost and effort needed to drop a 3700 in, id be more likely to drop a 1000 or 2500 in...