Beantown wrote:
Hi there,

Thanks for the preliminary advice. I would, in fact, be happy to do
the screwing - the problem is, I can't find any screw jacks for
purchase in my area! (I'm in Boston.)

The only ones that I can find aren't intended to screw as you go and
push things upwards. Instead, they're just "adjustable posts" that you
adjust to the size of the space as it currently is and tighten it up.
They offer no "jacking" aspect whatsoever.

Suggestions?
Thanks!

Use a hydraulic jack, then set the screws.

Also, just guessing, but I don't think you need concrete footings - just a
honkin' big sheet of thick steel.