The trouble, or problem, with Thompson's book, is that it never really gives "directions" per se, but describes what you need to do...

I have thought about all this myself, and I reckon if you put on the jacket, mark where the fell is on the jacket, and make the hem that length, then just cut the front so that it allows the sporran to hang freely... Also, you only need one button, and the pockets have to be moved up....

Using the pattern would be a big help.... Making the two sides of the jacket front perfectly matched is a trick......