It appears that an engine mounted on its side (9 o'clock) throws the lateral balance off some. Is the best way to counter this to put a bit of weight on the opposite wing tip?

If so, how does the plane react while in a loop when the right side weight is close to the fuse and the left side weight is out on the wing?

That's why it's called "balancing". Doesn't matter where the weight is, but the farther out you can put it the better because it requires less to balance.

There seems to be a mind set that all the stuff located inside the fuselage must be on or near the center line. I check the lateral balance before I install the tank {on gas planes} and RC gear. If the left side is heavy try mounting your receiver and batteries against the right side of the fuselage, often this will cure the problem without the need for ballast.