If you;re going w/ the 2.1 mount the rudder/elevators servos in the tail or it'll end up hopelessly nose heavy. Just finished one for a customer and it balanced on the money with a Saito 180 which is a good pound lighter than the Moki 2.1 plus muffler.

I'd also pin the firewall with some 1/8" dowels to keep everything together. Man, the vertical performance will be terrific w/ that combo, but I advise carefull throttle management on the down lines!