Greg, here's the measurements for the shelf:
If you download the photo and want to make sure that it's the same dimensions, just make sure to format the photo to be 4.125" wide by 6.3" high (that's 395.965 wide x 604.803 high pixels).
I've also attached a pdf. of a diagram of the shelf that should maintain the same dimensions, so you can just print the pdf and use it as a template. My recommendation is to bend the aluminum first, then place the template on the inside of the piece of bent aluminum and use the template as a cutting and drilling guide. That way you don't have to compensate for the stretch in the aluminum when it's bent.
Those little cutouts at the edges of the aluminum where it's bent were necessary for me because my bending brake is only four inches wide, and the piece is a little wider. The cutouts were just so the bend would be smooth; if you use a wider brake, or just a wider vise, you won't need those cutouts.
The shelf was designed to use an existing bolt and threaded hole on the inside of the frame rail under the seat, so you won't need to go looking for a fastener.
The aluminum is .080 thick; that's 12 gauge. I used that because I had a piece of it laying around, but you could probably go thinner. I'm sure that 14 gauge (that's .063", or 1/16') would work just as well.
Good luck.