I've recently finished a Senior Telemaster from a short kit.. Almost a scratch build, actually. A previous post said the tail can get twisty...

'Mo definitely...!

I tried putting diagonal braces throughout the tail area, etc. It stiffened the tail up... but not enough for my satisfaction. Balsa is so light and flexible, even braced, there's enough flex in the material...

If I were to build another, I'd swap in some spruce for center side and top pieces. I've got some pictures I can post when I get home tonight....

As for a motor, I can't say.. I built my bird to fly electric.

Picture #1... cross bracing put in place. I later added diagonals across the tail, where control rods would allow.
Picture #2... Adding the final center strip. It would be this piece on top, bottom, and sides I'd consider replacing with something stiffer than balsa...