Since it's plans, you have the option of building it lighter. Use the
lightest wood possible, put in a lot of lightening holes, use the lightest
covering. Usually the designers of gas planes don't really care of weight
because a gas engine has way more than enough power. With electrics you
really need to think about weight, airfoil efficiency and reduce drag. Also
if you have a grass field, you will need some extra power to get off of the
ground. I converted my 40 size trainer to electric just to prove that it
could be done and it cost me about $250 for the brushless motor, gearbox,
and speed control. Another $80 worth of batteries. It flew about the same
as when it had the $70 engine in it.
You could save yourself some headaches by purchasing plans or a kit
specifically made for electic motors. But if your like me and like
headaches, give it a shot.
P.S. While it's not completely accurrate give
a try, it
will give you an idea of what size motor you will need for your plane. You
could also give megamotorsusa.com a call and he could probably recommend a
good motor gearbox combination for your plane.