Modify the inboard end ribs as shown in the right side view of DWG 16A. The large hole for the access cover is bestcut using a flycutter on a drill press. Stiffener ring T-407 and access plate T-708 are supplied pre-punched. (The T-708 access plate is designed to mount the Stewart-Warner float-type sender offered in VAN'S ACCESSORIES CATALOG. If you wish to install a different sender, the T-411 plate is available without the sender mounting provisions). Clamp the T-708 cover plate on the rib with the flat forward edge aligned with the stiffener bead, and an equal distance to the top and bottom rib flanges. Drill all of the screw holes, clecoing as you go (be sure the hole for the fuel pick-up tube is oriented toward the top of the tank). Remove the T-708 and cleco the T-407 in place. Drill all of the platenut rivet attach holes. Remove the T-407, deburr all holes,
Used the fly cutter to prepare access hole. My drill press only goes down to 570 rpm, long story short, it made it interesting. I practiced a few times, and it cut a very nice clean hole. Fitted and drilled the T-411 cover plate. Fitted and drilled the T-407 and nutplates. Deburred all the holes.