This one is a real classic and classy laser! Introduced in 1966, the model 124 was part of the "Stabilite" series that included the 120, 122, and 123, and was characterized by the "L" shaped resonator common to them all.
This one is really old and must be from the very early years. Notice the cover that clamps on instead of using bolts, the beam pointing adjustment assemblies at both ends, and the cross-bar feet. The tube and optics are not original, but dayum .... this one made my month! Everyone used SP-124a or 124b lasers in school. All holographers from the '70s to the end of the century came across them. My finger couldn't hit the "Buy It Now" button fast enough.