Taking a cue from Mike, here's two pie pan Constellations that have almost as much difference as they can.

Stainless steel, date window, lumed dial and hands, full rotor caliber, flat bezel, and baguette indices with dog leg style faceted lugs from 1963:




18ct gold, no date, chamfered hands and dial sans lume, bumper caliber, beveled bezel, and arrowhead indices with tapered lyre type lugs from 1954:




Even the edges of the pie pan are different. The '54's edge is a simple 'crimp' (for lack of a better term) and the '63's edge is raised slightly. Only the crown, the applied metal OMEGA, Ω logo & star, and some of the fonts / ink are the same.