I flew my Ultra Stick 60 with an OS91FX originally. This is a similar engine to what you have. I only had to add about 4.5 ozs to balance it. It flew pretty nice. My ready to fly weight without fuel was 7lbs 0oz. Later I modified it and went to a Saito 100. I moved the servos back and was able to keep it at 7lbs 0oz even though I had done extensive repair after a crash which always adds weight. If I were you I'd certainly move the servos back, it really isn't that hard to do. I used carbon fiber push rods which are nice and stiff. Also I didn't have to move the battery much after moving the servos. I can reeach it with my hand. But you can cut a small rectangle in the bottom of the fuse and zip tie the battery to a small piece of plywood and just glue it between the fuse spans. If you need to move or remove the battery you just cut the covering and then cut the zip ties. I flew mine with an APC 15x6 prop. It flew real nice but you still have to watch full throttle because it can go way to fast if you're not careful. I can't believe you have to add 16 ozs of tailweight. That seems like an awful lot. I just can't imagine that. I would do something to make certain I didn't have to add that much weight.
Thanks,
Barry