So I think I'll go for 6 volt battery, my existing Hitec's which get 51 oz-in @6v for elevator and ailerons, and the recommended minimum rudder and throttle servos.

At 6 volt, the above will be at the recommended well-above-minimum required torque and good speed as well.

As for my Hitec prism RX, I could test that at 6 volt on a trainer before putting that in. If that's not ok, I'll just have to pull a Futaba FASST RX out of a small heli and then save up for a new FASST RX to replace it.

I'll perhaps try to get away with not getting a pitts muffler to save a little more. Looks like a normal 46AX muffler (with dubro extension) might fit inside the cowl. If I end up cutting up the cowl a lot, then I can get a new cowl later.

I suppose that's a fairly well balanced plan...

Cheers