Well, I built one with Unistrut and have it running now.
Made a couple of mistakes, but being able to reconfigure things easily was nice.
Biggest opps was it was too tall to go out the garage door when I wanted to get it out of the way… wound up shortening by about 6" and using those pieces as offset adjustments for the top bar… I left them “long” so that I could play with that position, although so far it’s been fine where I eyeballed it.
The castor mounts tend to flex a bit… I worked on that some today and they seem better, but may still have to revisit that. Doesn’t matter for machine use, but moving it around my “shop” it matters.
The back triangle is large enough to slide sheet goods in and store them. I’m going to put a strip of unistrut or a 2x4 across the bottom to keep the legs from trying to “fold” toward the center when I’m wrestling plywood.