Hard to say. I've never tried it. What's the part number for your tuner? Also what HP rating do you currently have and what model Allison are you running?
As far as the pcm's go, They should be one in the same but the tune on it would be different. I've never tried swapping a truck pcm into a bus, but I don't think it will work because the ecm looks for certain things such as a speed signal and pcm communication that a bus wouldn't have. Without the correct speed signal, I know you'll be limited to 2000 rpm, and without the pcm comms idk if it will even run.
Unless you have both sitting there, I wouldn't try it.