I looked over Matt Newsome's article, Pre-Culloden Tartans to get an idea of what all was going on with tartan at least in the ball park of 1773.

I also looked at his article, The Early History of the Kilt
The first instance we have of the pleats being sewn in to the phillabeg, creating a true tailored kilt, comes in 1792. This kilt is in possession of the Scottish Tartans Society and is currently on display at the Scottish Tartans Museum of Franklin, NC. It contains 4 yards of tartan, and has wide box pleats that are each sewn in. This is the first garment that can truly be called a kilt in the form we know it today. The tailoring and style are different from a modern kilt, but it is a kilt nonetheless, with its origins in the belted plaid of the late 16th century.
So the 1773 kilts would not have been tailored, and not at all like modern knife pleat kilts.

It also looks like this 1773 time period was within the Proscription time frame, though toward the end.