Similar to Iclang..........I would iron to a light weight fusible, adhere to a larger square, maybe even at a slight tilt, then do a blanket stitch with invisible thread. The blanket stitch is less likely to "cover up" the majority of the writing. Once it is appliqued, then square up all the outside squares to the same size and piece and quilt as usual. By adhering to a larger square on a tilt, you won't notice that the original 4 x 4 squares weren't square. Here is a baby quilt I did that will give you an idea what it will look like. This was made with a panel and each square was slightly different in size and none were square. Once they were sashed (you will be appliquing instead) it is not noticeable.
[ATTACH=CONFIG]522032[/ATTACH]