Am I understanding your blocks are 16 patch that consist of 2 1/2 inch squares? (4 x 4). You are not looking for a 16 patch block because you've already made them. Only needing to figure out sashings or how to assemble these blocks?
If so, then you could use just about any width sashing placing a cornerstone at the intersections. Is there any sort of pattern to the blocks themself?