Put some tire weights on top of the cowling to see how much you need to adjust the balance by.
A simple solution is to make the same wieght in lead into a plate using a couple/three cans of Play-Do to make a melting form for the lead. If you've got a torch-based weed killer (http://www.leevalley.com/en/garden/p...300,44822&ap=1
), this does a super job of hardening the plastercine while melting the lead.
Drill out a couple of holes to fit the mount, and put it on using some longer hardened-steel bolts.
I fly the electric version and I'm just about ready to try balancing it. Last conversion from an engine to a motor (slimer to electric) took 19 ounces of lead. That's the weight difference between an OS MAX .46 and an AXI 2826/10.