I found the perfect combination of spacer blocks among my kids toys. I placed these throughout the channels and then slipped the forward channels into place and clamped them down. Perfect 1 1/2" assembly the entire length!. Drilling the forward channel's flanges to the strips was a little easier since I didn't have to worry about the strips themselves floating around. I drilled both the inner and outer flanges to #40 first and then enlarged the holes to #30. The final task for the evening was to drill the forward F631E joining plate to the channels. This will eventually get riveted to the inside of the channels but it's easier to do the drilling from the outside.
