I screwed this step up pretty good, and John's help was immeasurably valuable in catching and fixing the mistake. Basically, I started off OK. I rigged a table under the left strake area using plywood and 2x4s to rig up a relatively stiff and sturdy (and perfectly level) jig table. I didn't know at the time that I could really have just skipped this step, but c'est la vie. Using the table as a guide turns out to not be as convenient as using the string-line method to align the rib leading edges, so I ended up doing that. My case was a little complicated because I'm also doing the extended strake modification, so there are actually two important lines to deal with. But it sure is an easy method to do. Sort of. I must have either been tired or rushed when I set this up because when John double-checked the left and right sides they didn't match. He ended up having to redo a fair bit of the layout work. It all worked out OK in the end, but this does underscore the importance of taking it slow and having as many eyes on a project as possible to catch mistakes. I'm sure I would have caught it, too - it wasn't exactly a subtle mistake. But it could have been avoided if I hadn't been in such a rush.