My experience with that model is that the lighter you can build it the better. It has a pretty thin airfoil and is easy to stall, which is why it snaps so well.
I flew one my brother had until he spun it in by doing an inside/outside spin too low, if it had a thicker wing or was lighter it would have survived.
I just was given one complete that had flown and is equipped with an OS 46 FX and Pitts muffler and my son is going to start flying it next week. We are retaining the glow engine for economy (I don't have to buy another motor, just a rx and batt!). It is box stock and has a 1/2 pound lead weight in the nose and the cg is right on. The servos, rx, and rx batt are all forward of the leading edge of the wing.
Sand every sheet of wood, use as little glue as possible when building the back of the fuselage, make the battery mount able to accept the batt right up into the motor mount (forward, or through the firewall) would by my thoughts if building an electric conversion from new. Also, engineer yourself a top battery hatch from the front of the canopy to the firewall or inclusive of the canopy, you'll thank yourself later (or hate yourself if you don't!).
P.S. I made big holes in the aft fuselage of one of my models, I cannot remember exactly the fuse layout on the Extra but it might by possible to open up the bulkheads and fuse sides to get rid of unnecessary material weight because the kit was for a pounding glow engine, you won't need a lot of that lumber. In fact, maybe some lite ply could be substituted with balsa?