hmmm, never seen it done before. Could be cool though.
Electric rcs dont normmally run a 2 speed tranny though, so you could eliminate that for simplicity.
A 650 could do it, but If you were going with new stuff, it might be easier to steal some parts off of an E savage and run twin 550s.

you've got me interested now...[:@]
I think I have enough spare parts and a spare magnum chassis to build something...