I accomplished the aircraft weight & balance today. With all fairings and panels in the aircraft, plus seats, carpets, fire extinguisher, and 8 quarts of oil, I used a plumb bob to mark the wing's leading edge (LE) on both sides in front of the main wheels, and marked that spot on the floor on masking tape. I then marked the exact center of each main and nose tire.
Knowing that the CG datum reference is 70" forward of the wing LE, I then measured the distance from the LE aft to the main tire center, and forward to the nose tire center. This gave me the exact arm lengths for each side.