Just quickly off the top of my head I wondering if you could make the blocks 5 3/4 or 6 1/2 and then cut them down to make them 5 5/8 or 6 1/8? Since both measurements are only 1/8 off from the easier size, I can't believe it would make any difference in the block. I would try making them with other fabric and see how they come out. I would bet that the block will look fine. JMHO