Quote Originally Posted by Hamish
Since you are not wearing a waistcoat - possibly they do not come with these jackets - your appearance could just be completed if you were to wear a Dress Belt with a rectangular 'plate' buckle. A belt would not, of course, be worn with a waistcoat.
To the knowledge, these mess dress jackets are always worn with a cumberbund in the US military, so no waistcoat is available. Someone with more recent experience could answer better than me. As a civilian kilt jacket (without all the military decorations), a nice kilt belt and buckle would look best.