When the FS was designed it was for a baffle .19 to .35 engine. With more modern engines this should equate to about .15 to .25. The Fox .35 stunt vibrates much more than a modern .25 like the OS LA.
I would second the LA or some other modern .25. The LA is available in CL version as the OS LA-S .25. Another available as CL is the Thunder Tigre .25 and the Fox .25.
If you opt to use the Fox .35, you might install a plywood gusset between the fuselage doubler and the wing LE on the inboard side to dampen vibrations.

George