I would probably just weld in a new axle shaft section of the triangle with one that is 5/8 rod and enlarge the leg holes a little. I like using the shaft collars instead of the caps as well - I have them on my MT grill. Thank you for the offer of help, I appreciate it.
We have a paver patio and it might be nice to put the 10" pneumatic wagon/hand truck tires on it. Same effort required but boy would it roll easy!