Even with the downthrust you will have no problem ROGing, but if the wheels are well forward keeping it straight could be problematical. Raising the motor thrustline might help, but a glow motor swings a much smaller prop than an old ignition engine, so prop size won't be an issue. As Dick suggests, part of the problem is the couple from a high drag centre and the excessive angular difference 'tween wing and tail. If you fit a rudder and elevator you change everything. You no longer have a vintage F/F but a sport R/C. If you want it to fly like a sport R/C then you can do a couple of things to help, reduce the wing tailplane difference to a degree or so, get the tailplane section as close to symmetric as you can, move the mainwheels back to just forward of the wing leading edge and the you can reduce the downthrust and move the CG to about 30% MAC. It'll still look like a vintage, but be much easier to fly in the normal manner. If you want it to fly like a vintage F/F then a moveable rudder trim tab is all you need, just to keep the thing in the same county, and fly it like a F/F.
Evan, WB #12.