nice work Brian. Ironically I'm doing the same thing with a grill for my 41 Willys. I have 1/4 in aluminum tubing and more or less have run into the same thing you did. I think the alum stretches a bit easier so it didn't buckel. The spacing is very critical as each error is multiplied as you go. Using the same spacers and clamping the same way goes a long way to keeping the error down. It is surprising what you can see if you step back 20 feet so it needs to be pretty good.
I made small mold that shaped each tube/bar then trimmed them to fit. I made little drill jig that cuts a fish mouth in the tube so the tube fit each other perfectly. A bit more work but in the end better.
I'm thinking of anodizing the grill some color but not sure what yet.