I presume that you are a Mason? There has been a tartan approved by the Scottish Authority for the Masonic Fraternity; you can see the pattern here http://www.kilts.com/freemason.htm
Why not show up kilted? There's nothing that says you can't meet your brothers on the level in a kilt. What's the difference between a well dressed Mason in a comfortable kilt or a cumbersome tux? One looks really good and comfortable while the other looks good but somewhat uncomfortable.
Just my 2 cents. Enjoy the day either way, and post pictures if you can!