My 65 c channel is made out of 12 ga plate steel that is boxed in ( another plate welded on the C to create a box. Had all the metal fabricated at a local metal yard. It was pretty simple. Im sure you can take a cut section to a metal supply and they could tell you. Post some pics.
Darkspeed,
My vote on this would be to find a salvage AS and buy the a frame assembly complete. If your measurements are off without having a live template, you could be making yourself a whole lotta headaches.
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