Dia Dhuit,

I think some of you are mistaking the Regulation Doublet for the Montrose doublet. The Regulation Doublet looks much the same as a PC except that it has Inverness flaps around the bottom instead of tails and gauntlet cuffs. It is worn with a bow tie and waistcoat like the PC. So, therefore you could wear a Regulation Doublet in place of a PC.