The outboard stiffeners are a little harder to hold in place because there are not any easy places to clamp. So like those before me I removed the seat floor and clamped the aft end to the wing 704 bulkhead using a piece of wood. I taped the forward end and clamped on a vice grip. Then I was able to reach thru the hole in the firewall and hold with line showing thru while I drilled. It took a couple iterations of crawling under and adjusting in order to get the centerline showing up thru the holes.
