Seems like most of the tension is on one leg of each piece of angle-section. I think the easiest way to figure out what size members you need would be CAD. If I get bored, I might model them up in CAD and do some simulations.3X3X3/8" is what I was thinking myself. Did you run calculations for that setup? Did you run calculations for the Coal Iron frame and find the calculations on the light side?
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