I'd get a CC BEC Pro, it'll handle the current with room to spare. Just make sure to disable the ESC's internal BEC if you use an external BEC. To do that, just pull the red (or brown, depending on the wire) wire out of the connector on the end that plugs into the receiver.
Ashleigh, if you have a 2S pack leftover from your ignition when it was a gasser, I'd run straight 2S through the servos (provided they can handle 2S). That eliminates a component, and thereby eliminates a point of failure.
I ran two 2s packs for my servos when it was a gasser, with a smartfly batshare module, would that still work?
Absolutely!!!