Wow, if you flip that chassis, you'll be the first I know of that's done that to a chassis that long! Norcal Bambi did that with his Bambi.. but that was 10ft shorter than yours. Not to say it can't and shouldn't be done... if you have the space and ability, go for it! You'll save your back. Visit Norcal's thread to see how he did it.
Now, in order of stuff - I'd separate the shell, and see how your c channel looks. If it's fine, then por 15, new wood if there's enough wood to make a pattern cut to shape. If not, then lower the shell to trace around, cut, then flip. But don't attach it.
You want the wood on first to stiffen it prior to the flip. I think the factory used the metal end plate that attaches to the body shell in the front and a rear cross memeber to attach chains and then rotated around the these piviot points. I think I have a pic of them working on one in an AS book around here somewhere. It might take a couple of days, but I could try scanning it and posting the pic if needed.
I was just thinking of your AS the other day, wondering how it was going?