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All the pics I have show the gun being lifted off, either by a crane, or various make-shift wooden frames with a block & tackle arrangement. That way all you need to do is lift the gun & drive the bison out from underneath, then lower the gun to the ground.
I guess it's theoretically possible to do it the way you suggest, apart from the fact that the fenders, on which your channels would sit, wouldn't take the full weight of the gun.
To answer your other Q, yes the superstructure has to come of either way, as the wheel hubs are wider than the superstructure.
