Maybe 50+ ounce inch servos (67 ounce HS-225MGs for my last one) and 4-40 pushrods will help. I generally flew the plane way too fast, and never had flutter. My first one flew on a Rossi 53 with an 11x5 APC and (in level flight) flew full power with no flutter. Also, heavy duty servo arms will help.

Put the CG at least a 1/2 inch (3/4 for me) back from the indicated spot.

Good luck,