Get the column perpendicular to the table. Then make the neg stage and lens stage parallel to the base.
If you are working with levels rather than mirrors, either shim the base to level, then the neg and lens stage, or use two levels and shim the levels so they read level with the base. Use one for l/r and one for front/rear.
Omega 4x5`s need the lens stage leveled first as leveling the lens stage changes the neg stage, Therefore you do the lens first.