Dale,
Here are two photos of my loader dolly, the yellow level is four feet long and included for scale.
In the front photo the top cross 2x6 keeps the bucket from sliding forward off the dolly or over-center of the wheels.
In the side photo the yellow level is on a dolly rail, that rail needs to be modified so it is flush on top for the loader parking stand shoes to slide along when mounting or dismounting the loader.
The cross member under the parking stand shoes needs to be repositioned under the rails so it clears the front blower mount & PTO bearing when sliding the dolly under the tractor.
Each rail needs to be centered under each parking stand shoe but the total width must still fit between the front tractor wheels.
The dolly wheels all swivel and are urethane on steel which rolls easily over concrete and haven稚 flat spotted over winter.
The JD procedure for latching/unlatching the loader requires the tractor front wheels be raised off the ground (or dolly) by the bucket cutting edge; this dolly is not strong enough for that too so I just temporarily slip scrap wood under it to take the extra load.
So far the best price I致e found for dolly wheels is at Northern Tool but if you need 4 or 5 dollies to store attachments it might be less expensive to just build pallets and buy one pallet truck.
Stay warm