No hands on experience with an Allison. But to drop a VW motor out of a car, you only need a few inches of clearance to slide the engine back.
On My Duchess, I accomplished that by cutting away some of the fiberglass on the rear valance (wasn’t much, and I followed the rough outline of the engine block. I have to remove the crank pulley before moving the engine, which by itself gains a couple inches of room. No clue if any of this will help on your Allison.
On my London Roadster (somewhat like a Daytona MiGi) only the rear bumper is in the way of pulling it straight back to get out. There is no “apron” around the bottom of the hatch that holds the spare tire. 1/2 the time I remove the bumper, 1/2 the time I jack it waaaaay up and slide it under.