With the engine at 8:00, I am concerned about lateral balance, since the single cylinder is mostly on the side of the airplane and the muffler mostly on the center of the plane.

It should not take that much on the wingtip to balance though but I am concerned about this...

I never add wing tip balance on these -that business of wing tip balance with a side mounted engine is really of little value .
The risk thru adding tip weight really screwing up dynamic balance is far greater.