I think you should have plenty of room for the hydro boost between the Allison and the frame. I am putting an Allison AT540 and a hydro boost in my 56 6100 the frame rails are 34"s apart, as with most big trucks and I am using a bracket that mounts the hydro booster and master cylinder to the frame using the stock pedal. I don’t know how the AT540 compares in size to the 1000 but I can tell you the 540 would be a tight fit in the trans tunnel of most pick ups and I have plenty of room so I think you will be fine.
