IMHO, in addition to a different/more efficient motor, you need much more cooling than you show here. Consider some ducting and baffling similar to the
photo below. The air exit needs to be 3X the area of the entrance.
On the motor choice. Turnigy HXT 50-65C = 414 gm, Hacker A60S = 595 gm,
A50L = 470 gm, Power 110 = 490 gm, Power 90 = 450 gm.
The reason the Turnigy fried was that it was running very inefficiently (63%).... see E Calc profile. I suggest you have a look at the Power 90 and a 16x10 2 blade prop .... see E Calc prediction (82%). Only 1.3 oz weight penalty