I suppose my first question is why would you bother messing around with a 9.0L for any reason.
While IHC does support their products better than just about anyone out there, even they eventually stop supporting their products. And it has been a long time since the 9.0L was offered so it has been a long time since new parts were made for it.
Most of those engines topped out at about 180 HP which isn't a lot of HP to move a big brick down the road.
They were not designed to work with a turbo. Adding a turbo tends to blow the bottom end out of those engines.
If you are lucky you don't have one of the engines that had a pump that would only deliver fuel to four cylinders at idle--a way in which to reduce fuel use but didn't really do anything except to make them idle really rough.
If you are lucky you don't have a leaker. They were very prone to leaking, particularly out of the oil cooler. Once they start leaking there isn't much you can do except pour oil into them or rebuild the engine.
If the engine is in a bus that you have already converted I would suggest it would cost less for you to purchase another IHC bus with a better (higher HP engine), a better transmission, and perhaps better axles with a higher speed rear end.
If you haven't spent much time and effort converting it might be better to just paint it a nice try and start over again with a better platform.
If you decide you really want to stay with what you have and just change the transmission, the 9.0L should use the same bell housing as the DT360/466 engines. It won't have the same bell housing as the 6.9/7.3/T444 engine.
Good luck and happy trails.