Have a look around the online stores like Tower hobbies or Horizon, a good number of new ARFs are being sold now that can be either glow or electric. Look at these to get an idea of motor, ESC and battery sizes you will need for your used plane.
Here is an example, it shows items needed to convert to electric at the bottom of the page,
http://www2.towerhobbies.com/cgi-bin...?&I=LXK971&P=0