Your link works. Did you see that they off substitution suggestions
From the pattern:
9.5 sts + 13.5 rows = 4” [10 cm] in Stockinette st (k on RS, p on WS).
From Bernat Softee Chunky:
11 sts - 14 rows = 4" (10 cm)
Suggested Knitting Needle
8.00 mm, US 11
It looks to me as if all squares are stockinette and if you needed to you might be able to adjust the number of stitches if for the correct size of squares. If you're doing the letters though, that might be a problem. Hmmmm.