Like others I really really really (that's three reallys on the really scale
suggest against changing this late in the game. Find a way to get those two other motors on there, you will be surprised at the difference.
AM has many ratios available for the toughboxes so you can also gear a little faster and still have good pushing power with those extra motors. At the same time you can reduce weight by using AM's aluminum gears and trading the box housings for the spacers also offered at AM.