You're right to make it direct drive. Geared props are great for climbing but this is obviously supposed to be a speed model and for that you need high RPM's and small props with lots of pitch.

There's enough torque in this that I think you need to treat the engine, shaft and support tray as a sub unit separate from the model itself. You may want to consider an arrangement similar to the speed pans used in the old control line speed models. But in this case the engine mount and shaft supports would be molded in glass and carbon fiber and form the lower half of the fuselage from the prop back to the engine. Doing it this way you could use the outer curves as a good basis for a stiff frame. Then a lot of stiffener bulkheads of aircraft ply with carbon rod or tube stiffeners to support the shaft bearing mounts. The bearing mounts should be made from aluminium for durability and the mounts should have flanges or fingers that allow lots of screws to bond them to the plywood pan.

Another option would be a slightly lighter pan with a machined out aluminium chasis to hold the shaft and bearings that then screws into the lower pan. This way the frame would ensure good bearing alignment and having the fram mount in the pan would help support the bearing frame and soak up a lot of the vibration.

At least that's what comes to mind at the moment.