Well the outside dimensions are 24x24, and the included sump has a footprint of 21"x18, according to Waterbox's website. I'm sure 21"x21" would work but I can't say for sure, the 70.2's haven't shipped out yet.
Yeah I don't see why not, the sump only takes up a portion of the height in the stand, would just need to configure the shelf to not interfere with the plumbing. Should be plenty of room to work with though