The heaviest implement I attach to my Kubota B3300SU is a Wallenstein BX42s PTO
chipper @ 420 pounds.
I rest the BX42s on a 36" X 24" caster dolly from Northern Tool. I mention the supplier only because it is difficult to find commercially produced dollies wider than 18".
Chipper is reasonably easy to shift around on the dolly but
before I made a simple spreader bar for the 3-Pt lift arms I regularly fouled one or both of the lift arms in the metal frame of the
chipper, lengthening the attachment process; shortening my temper.
I recently made a gravity-assisted lift arm spreader, inspired by a TBN post by "tractchores" titled: "Wallenstein BX42 Dolly Build". A simple idea but a big help in keeping the lift arms out of the way while maintaining a wide spread so they go one the pins easily,
most of the time.
My lift arm spreader is made from an old piece of lumber and two 8" MENDING PLATES from Ace Hardware.
I intend to build a larger caster dolly soon. I purchased four, 4" heavy-duty. bolt-on casters, used, on eBay for a really cheap price. Two of the casters swivel and two are fixed, the usual fashion on dollies. I am going to shop further and buy two more swivel casters for this new dolly, so all four casters will swivel for maximum maneuverability. Space in the garage is getting tight!
I hope this helps someone else.
Thank you "tractchores".