FYI, on page 23iS/U-04 when you go to countersink both F-01204J's make sure the top two rivet holes match the holes on the mating F-01204K-R/L's. All the rivet holes on F-01204J are symmetric except the very two top holes. I didn't realize this until I went to rivet the second F-01204J into place and couldn't get the rivets through these holes because I countersunk the wrong side of one of the F-01204J's
Mercifully I figured it out before I squeezed any rivets. I'll be ordering a new one tomorrow, but I figured this might save someone else from making the same mistake.