I'm not sure of the weight/wing loading of the Flivver, but the Saito .40
http://www.chiefaircraft.com/radio-c...sai-e040a.html swings an 11x6 prop at more than reasonable RPM, or, if you want more power, I've powered ".40 sized," 5# sport planes with the .56.
http://www.chiefaircraft.com/radio-c.../sai-e056.html
Love the Saito's for their dependability and price. I had a .56 that I flew until I had to replace the rings, replaced them, then flew it for another year before selling it on the model...