BB Auto Tranny Question

Just wondering what tranny I can use for my demon. I am thinking of doing a low cost buld, and I have a free BB motorhome in the back yard, I just need to pull the engine and tranny.

SO my Question is, can I use that tranny out of the motorhome? I would think it would be too long. Maybe something out of a C body? I know that there will have to be some mods to make an auto fit. Just wondering if the motor home one would work, and if not, what will?

If the tranny won't work, I have complete SB running gear that will go in it.

Thanks

Phil