Here's the pattern I used, Vogue 2383:
I had to modify the pattern a bit because I only had 2 yards of fabric instead of the 2 1/2 yards required. Turns out I just had to peg the legs by about 2 inches, which is pretty historical for the 20's anyway. Yay crisis averted!
Not a lot of other progress to show you, but I did want to put up some links I found that are helpful in making my pants:
Information on mens' pants in the 1920's.
A vintage set of suspenders.
A great tutorial on how to make a modern zipper fly into a button fly. Useful since the first zipper flies were in 1938.
An interesting look at extant pants. They don't have a waistband! They're called fishtail back trousers.
A tailor's blog showing some fishtail back trousers.
The mens' trouser page on the Morning Dress guide.
I'm trying to alter my pants to be fishtail, but I'm not too familiar with mens' patterns so it's an adventure. We'll see how my idea pans out!