Since the cub has such a short nose, I'd be willing to bet (a donut) that even with the batteries shifted as far forward as you can get them, it'll still turn out tail heavy.

But.. Like Charlie P. said....

Get it built first, and be willing to shift batteries as needed for balancing.

Oh.. what may help... try mounting the ESC under the cowl below the motor. You should be able to cut some of the lower cowling away for cooling. Like under the "chin" of the cowl. This could give you more flexibility when it comes to moving the batteries.