This tickled me, so I had to share.
I made the Whitney Jacket from thru-hiker.com back in 2004, but the sleeves were a bit short for me, and I didn't wear it very much. So, fourteen years later, after getting the idea from YouTube, I made some cuffs for it out of a pair of hiking socks that had shrunk. Worked perfectly!
I couldn't get the original elastic cuffs removed without damage, and they'd probably have leaked down anyway due to all the needle holes, so I ran a line of stitching next to the original stitching to contain the down, and just cut them off, then added 2-1/2 inches of the sock tops as cuffs.
I kind of wish the jacket had a hood...but I'd need a much larger sock