The old Futaba G series servos will work fine with the new FM radios..except for the one little thing you already found out, the center is off.
Futaba used to make a G to J sevo adapter cable that looked like a short aileron extension...I don't know if they still sell them or not. I have a few still laying around..I had Futaba do the narrow band upgrade on some old FG radios back around '91 when the spec became law and they threw some in with each RX they sent back.
So don't let anybody tell you they won't work (I've seen that opinion posted here), I'm sure Futaba wouldn't have went through the effort/cost of making these adapter cables if the servos they were adapting wouldn't work with the RX's they were adapting to
