IIRC, there are a couple different versions of the A-10. The one with the smaller motors and fans, the EDF50(?) version, can't be converted to brushless without some major modifications to the fan units. Those pinkie-sized IPS-D motors don't have a brushless "equivalent" that easily fits in the same mounting space.

The A-10 with the larger fan units with the "300" motor in them is an easy upgrade. You've got the Eflite 370 (4100Kv) and the Himaxx 2015-4100, which are both drop-in replacements for a 300 motor. Both will allow you to run a 3S LiPoly pack, which is the bare minimum I would recommend for such an upgrade. Why waste a motor's potential, I always say?