I just did this, and I had to decide exactly where to locate the blocks. The drawing indicates that the block is 40 1/2 inches from the number one rib. But the number one rib is 1 1/2 inches wide, as it is comprised of two ribs located 1 1/2 inches apart, covered with .8mm plywood which is 1 1/2 inches wide. Scott's drawing (scottiniowa here) shows the location of the holes in the block located as measured from the root of the wing, i.e., the inboard edge of the number one rib. The actual location of the jury strut attachment will be slightly inboard or outboard of this, determined by how you orient the fitting. The further outboard, the shorter the strut will be. Also, Leonard's drawing shows the tip of the fitting to protrude 1/2" below the wing skin. But I was worried that this does not give enough room to get the 3/16 bolt into the attach point, so I let it protrude more like 3/4 inch. I drilled the attachment hole in the tip of the fitting first, then drilled the holes in the block before gluing the blocks into the spar web. I had to glue a patch into the lightening hole that I had thoughtlessly drilled earlier. If I had paid attention to Scott's drawing, I would not have done this.
Jerry