The block uses 4 strips that finish at 2" each, giving you the 8" finished block. To get a 6" block, you would divide 4 strips into 6", giving you 1.5" finished strips. Adding the seam allowance back on you cut 2" strips instead of the 2.5". So the center 4 patch would be four 2" squares. You can construct the rest of the block like a log cabin.
I love this quilt when I saw it and put it on my list for next month. I want to make it in Christmas colors, and figure if I start in January I should be done by next Christmas.