Those look to be a pretty nifty idea.
I saved your images, (I hope that's ok). I have a Cal21 that I wanted to put up and I also have had trouble locating stands that are sutiable. Granted the 1,500 pounds I am planning to support doesn't compare to your needs, but if properly executed,
you should be ok. If you need to you can always make more. Noah's boat was held up with wood, no? Good luck and work with many hands. Jim B.