Made the rear strap mahogony blocks and glued in with T-88 also glued in the small 1/2 x 1/2 gusset blocks . All measurments are true to plan . The manual calls for a snug fit between the rib and strap block - mine where .820 to hold dead on at 26 1/4 between rear and main spar both sides where identical . WCP is dead on at 5/16 at the forward face of the rear spar on both sides per callout.