After the great advice on here, plus a bit more research I've decided to go DOM round tubing on the frame. With the advice here I've gone up to 1 3/4", .134" wall for the main rails, 1 5/8" .110 wall for the cage main hoop an halo, then 1 5/8" .083 wall for the rest of the cage. It will increase weight, but minimally and the added beef will be good for that possible day when things go terribly wrong!

Yeah, I'm making a lot of extra work for myself by building a round tube frame vs. a rectangular tube frame but the difference in weight (over 1 lb. per ft.) makes it worth the extra effort in my opinion. Nothing is final yet, the tubing isn't ordered yet, so further input is much appreciated. I really wanted to have most of the chassis and cage done by now, but just too many other issues to deal with this summer. Oh well, no time limit on building your own stuff, right? Hopefully I'm able to get these other projects complete and enough room and time to get going on the '57 this fall.