[RC-Monster Mike]

The balance pro packs would work as well, but the advantage of the scorpion system is the fast charge and built in balancing/charge/discharge cutoff. I would use a series connector from the controller(as described in the "how to program your BK controller" post stuck at the top of the brushless forum.
I did have to countersink the new mounting holes. And a bench grinder/dremel would work fine(this is what I used, as I did not have the mill when I did it).