Besides squareness also check for excess toe-in or toe-out of the hulls, which should be parallel. I beach-crewed for a good friend of mine who was in the disastrous Worrell 1000 start at Jensen Beach in 2001, and ended up sailing 800 miles with enough bend in the main beam that the bows were 4" closer together than the sterns. We checked so many things, and replaced so many parts, but somehow missed that little detail (for ten days!)