Classic Stern and Bally are all 28.5 Inch. Stern are a gun metal hammertone finish with no ribbing, and Bally can be charcoal or black (Space Invaders) with no ribbing.
Classic Williams are 28.5 Inch, chrome, no ribbing
27 inch are usually Gottlieb, in Chrome. 31 Inch are also Gottlieb. From memory, there is a Gottlieb 29.5 Inch that was used on Black Hole and Haunted House (maybe more titles).
A VERY rare Bally leg is I think 31 Inch black leg used only on Bally midway, Dungeons and Dragons and Escape From the Lost World (maybe more).
What finish are your legs ? Chrome, painted etc...