There is only one question to ask. As you are not going to be a member of the "inner circle" at the wedding what are the guests wearing? If it is formal day wear with morning suits, then the kilt(tartan I presume) equivalent is the black barathea, silver buttoned argyll and that is the way to go. If the guests are wearing lounge suits then a tweed argyll with waist coat( or,any kilt day wear jacket in tweed) it perfect. If it is more informal then perhaps just the jacket ,or even just the waist coat.

As we only(I think)have day weddings in the UK a good rule of thumb is: never ever a PC for a wedding. The only possible exception is if you were ONLY going to the evening bash, if there is one.