There are many Allison Transmissions that will work with the cummins 5. 9 or 8. 3.
The smaller of the the mechanical transmissions being the AT transmission (production stopped 8/1/03) is a very good transmission for a cummins 5. 9 mildly bombed. It's a little bigger than a turbo 400 and it's much stronger. Since it's a hydraulic trans, it's very easy to adjust shift points etc. Main and Line pressure can be adjusted via stiffer springs etc. It's a 4 speed and comes in many different ratios. No overdrive though. Would be good with an overdrive box.
The next size up is the MT. Can't recall the exact horsepower rating. It can be found in many motorhomes and similiar duty platforms. Can be found in many configurations, close/wide ratio 5 and 6 speed. 5 & 6 being overdriven.
And the mother of all the mechanically controlled ON road Allison's, the HT. The HT if i recall can be had in 4/5/6 speed configurations. It is very big. This can be found in tri-axle dump trucks, semi's, Agricultural sprayers (Big A etc. ), cement mixers, etc. Very high GVW rating, and something like 2000 lb/ft input torque max rating.
All of these now have an electronically controlled equivalent.
The AT was replaced with the 1000/2000/2400 series transmissions. All the transmissions are available with various bellhousings, including SAE #2/3 and the 1K/2K/2400 series has a GM bellhousing for the duramax and 8100.
Now, what most people don't know. . The new electronic allison's will operate with older mechanical diesels. The allison gets it's throttle position sensor information from a TPS sensor attached to the pump lever arm.
Whereas the electronic diesels will transmit the TPS information over the Controller Area Network, CAN BUS SAE J1939 network, or a serial data connection, SAE J1850. There are also other standards, just can't recall them at the moment.
Hope that clears up some of the mysteries of the Allison's and how to adapt them.