RE: Gas to electric swap
You're probably looking at about 3.5 pounds ready to fly with electrics. Sounds like the plane would call for a .25 glow, right?
The power system will need to be in the 350-400 Watt range. I recommend a 3S LiPoly (11.1V) of at least 3000mAh capacity, and an AXi2820/10.
I'm not so sure about the batteries you have, though... They're the old LiIon from your description, and won't take the 35 Amps you'd need to fly the plane well.