You know,

I am just about finished with the Tubs in my '35. I thought the HammerForm way would be the best also, so I made one up using MDF, locating pins, and clamped my 18 ga. CRS to it and bent it over. When I got it out, i had a LOT of deformation (I used a Slapper and was gentle as I could be). I straightened out the deformation with a Hammer and Dolly, and had to use a Shrinker to pull it into line, but just wasn't happy with the results. So, I have a HF Bead Roller and got a set of Tipping Dies from Hoosier Pattern, rolled in my Beads and then tipped the angle (it's actually easier to do than to try and describe the process here). Then I helped it over at about 10 degree intervals so that the curve was at 90 degrees-took 1/4 of the time that a HammerForm did and a bunch less deformation.

Now, if I were to form the Flange you are looking for I would get a set of Round Over Dies from Ron Covell and make the transition you are looking for-just my .02 worth-