For attachment ideas, take a look at this thread.
https://ck5.com/forums/threads/a-better-way-to-remove-the-hardtop.240634/#post-2344611. I used these "bed bolts" to attach the roof rack I built. I've lifted the hardtop from those mounts and have walked on the roof rack many times with no problems. I would only trust something like well-nuts for light duty stuff.
It should be easy to build a rack like that, as a single hoop of EMT and 4 pieces of angle. There are also a lot of racks from places like Thule or Yakima, that may not be "for" a K5, but dimensionally could be made to work.