Since I do not have access (anymore) to a machine shop for precision built parts, I have become a fan of designing everything to be adjustable! The scissor lift mechanism you mentioned could work. The "Leveling" adjustment I would use for each of the four corners would simply be an eccentric mounting method of the actual table-to-scissor lift mechanism. This could be accomplished with a common drill press. Simply stack 4 round pieces of plate steel, and clamp them together. Drill a center hole through them, then an offset hole (to serve as the actual eccentric). Disc brakes work so well on an automobile because of the clamping action against the brake rotors that they use. So, the locking method to employ here, would be to design the discs to be locked with either a second piece of plate, or a large flat washer using a bolt which would be threaded into the actual frame of the table. A lever could be attached to the outer perimeter edge of the discs (either tapped into the edge, or welded onto it) to allow for ease of adjustments in leveling each of the four corners. Or (since this SHOULD be a one-time only operation) a simple series of holes could be drilled into the perimeter of the discs, into which a small allen wrench, or punch could be inserted and used as the handle to adjust the position of the "eccentric" for leveling. I really miss having access to the machine shop where I used to work. But since the plant closed, I have learned MANY ways of achieving precision designs by simply designing the machines I build with similar adjustment mechanisms. There IS more than ONE way to skin a cat!