I have a few regulators from HK. They work great.
http://www.hobbyking.com/hobbyking/s...ator-UBEC.html
With a Futaba R617 I'd recommend 5 Volts, not 6.
Just make sure you hook them up between the switch and rx, not directly to the battery. They would drain it when not in use.
Make sure it can deliver enough current, a 3A regulator can not feed a large plane with digital high torque servos....