I do not possess the model (I hope to get one at Salute).
Looking at the instructions, the method of joining the upper and lower hull appears to be different from all the other Rubicon kits I have assembled - the others have two plug and sockets which allow you to take them apart, great for spray painting and when you decide to make last minute changes (see my Panzer III). This is true of the M4A3 kit which also has a removable differential cover.
If you can assemble the hull in a similar manner, you could modify the ammo racks to allow swappiing, however the gun's travel lock is different
You might be better off just building an M10 and an M4A3 and swapping the M4 turret for the M36 turret, giving you an M4A3 or an M36B1.