ORIGINAL: 4-Stroke
I just finished a Big Stik 60. I placed the 70 Magnum 1 Inch closer to firewall and batteries etc. as far back in the fuse as possible. It still needs 6 oz. of lead way back on the fuse. Input
Aside from installing a larger, heavier engine, you could try relocating the rudder and/or elevator servos to the rear of the plane.