Hi Pete
Hyperflight used to do a BEC designed to be connected between the receiver and each servo. For your set up, if you were to go with a LiPo of LiFe battery, you could power the Rx and fuz servos direct from the battery. For the wing servos, which are a lower voltage, you could use the BEC connectors to reduce the voltage to 5v.
Problem is I dont see them on their website anymore. They still have a picture of it under the Electronics heading but when you click into it they only have the magnetic switches (its the image for Lipo Regs & Switches).
Personally, I would always use servos with the same voltage ratings. I wouldn't mix high voltage and medium voltage servos together. Others might say its fine, and it probably is with the switch in Andy's link, but I think keeping it simple is the way to go.
Earlier in the thread you mentioned you wanted the 4kg torque of the 6v Bluebirds. If it was me, I would get 2x Bluebird BMS-390DMH servos for the fuz. At 4.8v they are rated to 4.6kg so more torque and you would be able to use the 1600mah battery in the image above that will fit that nose perfectly. Only £24 each at Hyperflight so wont break the bank.
Plus that means both your wing and fuz servos are 4.8 to 6v so if you ever wanted to go 6v it would be fine. The components shop have a note stating they can do custom packs. I doubt they would charge too much for a 6v 2/3a pack with either a -== or --III design and that should fit your nose.
Hope this is helpful, as that was the intention.
Brett