The method calls for first making a chalk tracing of each piece on muslin. Here's the pocket:
Of course, it wasn't really all that simple. There are all the fiddly bits that make up the fly zipper thingy and were a real pain to figure out. But I did it and they are wearable. Also some of the worst sewing I've ever done.
The fabric is a lovely lightweight stretch denim from Emma One Sock, and was a joy to sew on. Next I'm going to make some gray cords, which should turn out much better, now that I know what I'm doing.