Since you already have the support equipment for electric flight it should be a lot less expensive to go that route.
The motor and ESC recommended for the Top Flite ARF are about $100 each.
http://www.gpdealera.com/cgi-bin/wga...T=2&I=TOPA0906
The Top Flite kit has about the same weight estimate as the ARF so these items should work for it.
For batteries the specs say '11.1V 3200mAh LiPo battery & 7.4V 3200mAh LiPo battery' so your existing packs may or may not work.