Hi Steve:
Did some comparison weight vs thrust and my first choice would be the Jets Munt M70 more thrust and lighter than the King Tech k70.... The K85 is a pretty heavy piece of machinery. then there is the larger fuel tank you need for the K85. since they are mounted pretty far back you may need to add dead weight to the front to compensate
for the C of G. For any servos mounted in the tail look at the MKS 737 or the 747 servos for power for a 38 gram servo.