The best way to check the CG is to fly the plane into the wind and pull up into a 45 degree upline, then roll inverted and take your hands off the sticks. The nose should just barely begin to drop off. If the plane climbs, (remember you're inverted), then the CG is too far back. If the nose drops bad, the CG is too far forward. Once that is set, when you fly inverted straight and level, you should use very, very little down elevator to maintain level flight. All of this is assuming your up and down, and side thrust is correct, and all incidences are correct, otherwise you're trying to trim out bad tendencies being caused by an airframe that is not straight and true. Once you know that is all set, then you can start trimming for multiple rolls (5 or 6) to the left and right without losing heading. That will set your aileron differential. That is also done on a 45 upline into the wind. You need to do all of this at full throttle, because that takes into account the full engine torque being produced. This is how how we trim the big IMAC gassers, and when it's trimmed out, it will be a real pleasure to fly. Good Luck.

Ken