The regulation doublet is highly tailored - in the photo you can see that on the back there are four curved seams which end at the armscye, two each side.

If your original jacket is not shaped in that way it might be difficult to create it, though if the jacket has an armhole deeper than the doublet's then it could be an advantage to be adding that shaping.

It also looks as though there is a dart in the back of the sleeve cap.

Creating a hybrid might prove problematic, as the PC has a centre back seam and the doublet does not.

Personally I would examine the original tailcoat and go for a conversion to the one which is closest to its present construction.

Anne the Pleater :ootd: