Darrell,
Welding rod would certainly be strong enough but would'n't that be rather heavy? An alternative would be either arrow shafts (my personal favorite) or carbon fiber shafts. Both have more than enough strength at a fraction of the weight.
As for the dual servos on the elevator, I, unfortunately, experienced the failure of a solo elevator servo on a final approach. Let's just say it wasn't pretty. Dual servos here would be a real plus.
As for the mid-mounted engine location, yes, a bit of engineering would definitely be in order. And the one who perfects it will be a hero to all who desire a scale P-39 or P-63, that's for sure! The driveshaft location is why I considered the use of the prop reduction unit in the nose per the full-scale aircraft. More engineering. For the purist or scale competitor, this would be a wonderful challenge. But for most of us, this would be an exercise in frustration when all we really want is a knockout plane to fly on the weekends.
Back to the building board, Darrell. Post those pictures!
Al