My son found a good 27 cowl out in the desert south of Bonneville, no cancer,, We are still looking for a back good half. I have enough projects and don't want to do as much patch work as you did. Another son wants to build a 27. When I built the deck lid for the 29 nash I made the inner structure 1 1/2 inch smaller then welded flat strips hanging out.At the time I thought I might want a rain gutter and weatherstrips I then laid it over the hole and scribed the opening, then trimmed allowing for the hem overlap and gap. I clamped the skin sheet over the frame and scribed it then used the brake to just make slight crease for the sides. The college has a magnetic brake, It can work like a pan brake, Lay the sheet on the table, line up the marks then put the top clamp irons on and step on the pedal The Electro-magnatic holds it down to bend large pieces like you can do with a finger brake. I did a 90* plus bends on the top and bottom , hammered them down a little then used the brake to crimp them, the slight crease on the sides gives a good hammer line to hand work the sides. I watched a couple guys over work their projects on the english wheel and get too much crown . I took the easy way out and punched 105 louvers .