I would square the blocks to the smallest measurement. Then I would take the ruler and trace it onto some of that plastic that you can use for templates and put in the marks. Then I would trim the plastic (carefully so the lines are in approximately the right place) to match the size of the blocks (and mark the size of the block on the template) and I would then use the template to cut the twister blocks. I have done this several times when I have found my starting pieces are not the same size.