Adjustable-height, side-mount, heavy duty casters? Need to move a heavy air compressor

I have this 900-lb air compressor on a wooden base I built. At the time I built it, I was able to move it around using a pallet jack. But now it's in a room that's too small to accommodate the pallet jack, and I'm looking for another way to maneuver it into position.

An ideal solution would be a heavy-duty adjustable caster I could side-mount to the platform. I imagine something with a long, threaded stem and a hex head, and a beefy bracket that can accommodate lag screws into the side of this base. Then I could just use a wrench to lower them (thereby raising the platform), push it into position, then raise them back up to lower the compressor. But after an hour of googling, I haven't found anything sufficiently sturdy to do the job.

In the photo you can just make out these three-wheeled dollies. I was going to try to jack it up onto those. They're only rated for 200 lb each, but I'm hoping they'll last long enough to let me put it in position.

Beyond that, what suggestions do you fine folks have?

(P.S.—I had a really hard time finding a tag for this post.)

Update:

I found something called a jacking caster. These are awfully expensive, but it's more-or-less what I was imagining.

Update 2:

Ah! Yes, searching for "jacking swivel caster" is yielding results: http://revvocaster.com/index.php/whats-your-application/40-jacking