There are variances from kit to kit, but I doubt a 2 pound chunk is needed.
Without re reading the manual is there an option to put the rudder on pull pull or is located in the rear?
I asume its balanced upright on the top wing, with measurement near the fuse, not wing tip??

EDIT read the manual

If you go 6.5 , will it even come close to balancing, upright, inboard on top wing??