Hola Amigo,
I have not received alerts to post replies on this thread, so I only saw your question today when I decided to check the site. I am still on the Hostettler 33% scale SD thread.

I dont think you should make the Pilot Super Decathlon scale smaller for the OS 120 - this Kit was originally designed for 60-2C or 120-4C engines.
Those who built it for gas engines had to beef the structure up to cope with the greater forces and vibration. SO if you build it exactly per plans you'll have a strong, lightweight 1/4 scale airplane.

I don't have the drawings of the Pilot kit, but I have a similar design of the Citabria, which could easily be modified to a Super Decathlon by making the ribs semi-symmetrical.

If you're still interested, please let me know and I'll send you a copy.
Dame tu direccion y te lo mando.

Marcus from Brazil