Maybe I should just get a gasser.
Could make that flybarless for $60 with an RJX .50 head.
The MKS servos I listed operate at 120hz, the closest thing to that on the Robird G31 is 125hz, not sure if the extra 5 hz would cause problems.
What about these servos? (if you add these to your cart they are actually $18, although it doesn't say so, these *are* the digital version)
Ino-Labs is a good brand (I have Ino-Labs on my FBL 450 Sport and have never had problems with them) and some people have said that these servos are acceptable for sport flying and soft 3D on a 600 size helicopter. But I'm not sure about FBL. It would make a good throttle servo though.