Temporarily Attached F-804 A&B after fabricating spacer blocks made from a red oak 2x2.
The instructions had me baffled about the spacers. The dimensions, other then the specified width, were not explained. The instructions say to make two spacers where a spacer is needed for the top and the bottom of the center section to maintain the width of the wing spar to fit later. In stead of the four spacers that I envisioned, Van's support said that two spacers were enough because one spacer should be made long enough to extend from the upper hole to the lower hole on each side. Having made four spacers, they said that would be fine.
The width was carefully sanded on the belt sander to a width of 1.428 inches. While bolting the F-804 pieces together, I avoided compressing the wood spacers.