This may or may not work in your case, but I welded 3/4" nuts to the bottoms of my car stand legs & double nutted bolts to adjust the stand to set level and make up for any dips & high spots in the floor.
I did the same thing when I built the jig for the chassis. In that case I got the jig setting solid & level using the "bolt" levelers & then cut some "L' brackets out of 6''x4'' angle and bolted/lagged it to the floor. I left the "L" bracket slightly off the floor so I could draw the jig down firmly against the leveling bolt with a tapcon into the concrete. That might work too if the stage will be a permanent fixture.