[sdstriper]

Most of the buses with the 6BT/Allison 4 speeds were 1:1 final drive ratio, unless you get lucky and find a really recent one that has OD. I wouldn't buy into the Allison is tougher than ??? whatever brand you insert either, they do burn up too. There is a reason Chrysler used their own transmission in the Dodge trucks, same thing with the Getrag that often gets a bad rap, fact is NV4500 is not as tough but is definately more popular of a swap when rebuilds are considered. Your best bet is to buy a donor vehicle that has an OD trans. and your going to want to keep the rpm around 2k when considering axle gearing. I know a fellow who has done a bunch of conversions like this one. Very good conversion for you, nearly a direct bolt in with the right donor.

 

[sdstriper]

I would look for a 94-95' Dodge Cummins, 4 speed auto w/lockup converter, 3.54 axle. Wrecked etc. You can run that trans, with or without the PCM. Lockup converter is huge for economy on the road. And the lower numerical(higher) gear ratio is also, this is a torque monster remember, gassers needed that 3.73+ to get that lumbering beast moving.