CG's are usually about a 2.5 : 1 ratio between the tail moment and the nose.

So if you move a 2 oz servo from the tail you roughly gain 5 oz in the nose. Or said another way it's like adding 5 oz to the nose.

Of course you have to add a pushrod to the back so you would get about 4 oz in tail weight relief. With all of the stuff (battery etc) forward you would probably balance. I can't promise you that because each plane is different.

I have seen many Quests running with lighter 2-c 91's and tuned pipes, or not. They all balanced. I can't guess much more than this.

Regards,

Eric.