Have you considered welding (or bolting?) square sockets into the bottom of the frame and then putting jacks underneath into those holes?
I definitely see the issue. You should be easily able to weld onto some of those square tube jacks with a square pin to go either inside or over that tube and pin in place.
I would still start with the HF or Home Depot or Napa adapter and cut off the unused bit then weld it to the back of a square tube Jack.
I also wouldn’t pay someone the money a pro welder would want! Gifted amateur is good enough for this job!
You could also drill a set-screw into the round mount on the front Jack to take out the slop?
I definitely see the issue. You should be easily able to weld onto some of those square tube jacks with a square pin to go either inside or over that tube and pin in place.
I would still start with the HF or Home Depot or Napa adapter and cut off the unused bit then weld it to the back of a square tube Jack.
I also wouldn’t pay someone the money a pro welder would want! Gifted amateur is good enough for this job!
You could also drill a set-screw into the round mount on the front Jack to take out the slop?