I don't think so, I mean from a fluid aspect yes, but the interface of the transmission is not even close to the same, the torque converter is not a floating unit like a car, the torque and horsepower curves would be totally different, the transmissions are doing entirely different things. I am not ruling anything out, but I suspect even the people dealing with the Allison 1000 series (think duramax) would shy away as the interface is different. The books I have discuss how to pick a torque converter, so I need to pick the brains of some Allison tech guys.
The funny thing is the integration with the engine seems to be the easy part, then you get into the ABS and any traction control, that seems tougher, I will need more info from the manufacturers of the other equipment to figure that out.
What I do think is that if you get the right torque converter for the engine, after that, the programming calibration is less of an issue, most engines turn between 2100 and 2300 RPM, I will have to examine how my trucks shift, I am pretty sure they actually shift at the governed RPM under full throttle, I know light throttle they shift at much lower RPMs. These transmissions can be programmed from Allison to be 4 speed, 5 speed, or 6 speed depending on the application, it all seems relatively arbitrary and based on the end user. The driveline definitely comes into play, the rotating speeds will increase significantly going from a 4 speed to a 6 speed, but most trucks were designed to do highway speeds and almost any truck can be governed by speed rather than just RPM, even I would probably govern my speed to 80, no need to go faster than that. My goal is to get the normal driving range into the fuel economy area of the engine, thankfully this also puts it into the power range you want so passing or hill climbs will be efficient and powerful. Most of my trucks currently are geared to the RPM governor and that stinks, having another gear or higher rear end gears would allow me to be at a much lower RPM and still have plenty of power for the fun feeling.
The detroit 50 series (4 cylinder) has a strange power band, after driving the truck that I didn't want to buy yesterday it was apparent that the engine is designed around fuel economy. It reminded me of my 6.5 diesel in the burbs, not overly powerful, but plenty to get the job done. The 50 series has plenty of torque to get you moving, but the horsepower appears to come from the turbo, so you have some perceived lag, yet the engine is steadily moving you forward, I suspect it doesn't change much loaded as the torque is really what gets you moving, the horsepower keeps you going after that. It may be that the turbo can be upgraded, generally this hits your fuel economy, so it might not be worth it. Regardless, I was impressed enough with the truck that I am still moving forward with my project. Just to let you know, the truck I test drove had 875k miles on it. That has to be the most miles I have seen on a "light duty" business class truck, it made me feel warm and fuzzy.