Something to take note of: The big rig service shops, at least the good ones, always replace the rear main seal in the engine EVERY time they remove or drop a transmission, for whatever reason.
Given the way the Cummins likes to leak there, it's a good idea to go ahead and do that even if it doesn't look like it needs it. IT WILL NEED IT LATER, guaranteed!
Second reminder: Do not try to detach the bell housing from the transmission on the six-speed. It forms the front cover of the transmission.