Hi Steve,

If the two motors do not exceed the maximum capacity of the ESC, it will work.
How good it'll work depends on if both motors run equally smooth, most of the time one will run slightly faster than the other.

A relative small boat like the Baltek will perform better when you add one cell (7 instead of 6 cells).
Also replacing the steering outdrive with a seperate rudder will improve the performance.

I've seen a Baltek being "improved" by putting a 700 motor and 12 cells in it, the boat nearly sinks, but once on the plane, it's a (hard to control) projectile...

Regards, Jan.