Here in Italy we are, perhaps, a little less rigid in application of the rules, not only about higland dress, but for every type of dressing.
Here, if the groom (right?) is a close friend you can choose and if you like it you also wear the equivalent of a highlander shirts with or without swordman's or potain's vest, kilt, hose and Ghillie brogue.
If you are the best man, instead it is requested a more formal dress at every moment of the day, so jacket and vest shouold be obliged.

Owing to our way, PC it is almost too much even for marriage (if you're not the groom), because we pay attention to be a less formal and elegant then the groom. For this reason I did not bought a PC, but a different and more informal model of jacket.

Smoking and tight are not so used suits here in Italy, only in really few occasions

Some weeks ago I attended to the marriage of a friend of mine:
I had the kilt, formal shirt, tie, and an italian black jacket (my wallace jacket it is still in Scotland....). I was in the stanadard of elegance of the marriage!.

Ciao!