Some items of information you may be missing.
The T444E is SAE2 by default, but most of these on Buses come with a SAE2 to SAE3 Ring converter which also adds length to the whole process.
You may require a new flywheel and potentially torque converter as well to make it fit directly and work.
I've not seen anyone really try to just bolt directly SAE2, but Cadillackid who knows these pretty well stated that it may need a new flywheel if you attempted this. So something to consider.
Another item which makes this difficult is that your 97 ECM is J1708 protocol, and a AT2500 expects a J1939 protocol. So your TCM will not work directly with your bus.
I know the struggle, as I'm in the same boat.
To fix this protocol issue, you need an AU device which can translate what the transmission needs from J1708 to J1939. This is needed so the live RPM data can be sent to the TCM on the transmission to know when to shift gears.
Another problem is even if you wire in this J1708 to J1939 AU device, now you have a throttle position issue. You have to get a specially made throttle controller added so it can show you the position of your throttle because the ECM won't communicate this accurately to your TCM. CAC Customs makes this device. Google it.
Additionally 2500's from small consumer trucks don't fit unless they are labeled as SAE2 or 3, if it's from a large medium duty haul truck it will.
We talk extensively about this replacement process here:
Adding J1939 to a 3Box Bus.
I provide a wiring diagram to make it work, and the Bouje guy on there actually took this diagram and ran with it without us actually testing it lol, but he reported back that it did work for him.
Also I would consider getting instaed of a 2500 Allinson, get a AT1000 with 6 speeds and 2 lock up gears from the years 2006-2009. It's likely the best replacement for your setup with best ratios.