I have moved many grand pianos over the years.  I will sometimes place
the dolly under the grand skid board, toward the end away from the
keyboard, since I do not carry large blocks with me.  That also gives
about a foot off the floor when I have to pick up the grand to center
the dolly.  I also do not center a dolly but place it a little off,
so I can turn the piano by pushing down on one end of the piano.

My dolly has no swivel casters.  It is made by New Haven Moving Supply
Company for pianos.  One man can usually move a piano with one their
dollies.  Call out store and they will tell you about the many times
one man has moved a grand by himself with these dollies.

Don Teach