8A36,
Be sure that you baffle the cowl, so that all of the air is forced to go throuh the fins. Make sure that the cowl exit area is 1.5 times the inlet at the fins and the open cowl flaps should help draw out the air also. This should solve the overheating issues. Also as mentioned above, use a 24x12 or 26x10 prop and it should get close to 6,500 rpm. The flywheel action of the larger balanced prop sould help reduce vibration. Timing and mounting need to be good as well. Good luck.

Dave

PS: The typical carb has a spring on the throttle shaft which prevents vibration from allowing thr throttle to cruve the throttle bore. Check for this.