60 mph mamba brushless setup for e-maxx, would this work?

What is the preoccupation with dual brushless motors lately? Running two motors won't necessarily make the truck go faster. Especially considering that you are talking about running XL motors with only 12 cells each. The motors won't be turning very high rpms and they'll have to be moving all of that battery weight.

Perhaps a better way to go about it, with the equipment that you mentioned, would be to run a single 7XL on 15 or 16 cells, depending on what your MM can handle. I have one that will do 5S lipo very comfortably.