You can use two wheels with locks that swivel to steer with and 2 of the same size that just lock. I've used them and they worked for me. I put them on a wooden stand for a jointer.
The wheels can be retracted using threaded rod, 2 nuts to fit the threaded rod, 2 steel plates with the nuts welded to both while on the rod. Plates should be welded to a length of black iron pipe to give clearance to the threaded rods. You would need 4 of these sets. I think it is not worth it...
I've spotted a really large stack of pallets that have been there a long time where I get my chicken feed. Today I'm asking about hauling some of them off for them. The first thing I need to do is build some easy make chicken box nests to put on the ground in coops for broody hens.
My wife and I are approaching #59. She might get a pallet project for that in the way of a porch planter. I'm looking for pallets now. I think I can also build some nest boxes out of pallet wood.