Hi Josh

Of the options you've listed the one I'd recommend most is redesigning the chassis. One issue with the Carbide/Tombstone style bar spinner is you have to sacrifice a large portion of your internal space for the weapon as it spins. Also keep in mind you will still need room for a weapon motor as well as the electronics. If you're desperate for space you could mount the wheels externally.

Changing to smaller motors is also a viable option, if you haven't bought the 45E's already. I use common HRS-550S 18v drill motors (Gimson sell them too) & they haven't let me down yet, even when the rest of the bot was falling apart around them.