The Zorki 4 was made longer than any other FSU camera. Don't know how many variations were made but over ther years they kept trying to find ways to make them cheaper--nylon cover, painted numbers and bane, etc. And if you snap the shutter on a 1950s and a 1960s Z4 the sound gives the impression that the 1950s model was built from heavier material.
My favorite is the Mir which is a Z4 with out the slow speeds (who uses then anyway?). The shutter speeds only are marked to 1/500 but 1/1000 is there on a notch that isn't marked. Maizenberg, the expert on Soviet cameras said the Mir is one of the best because there is less to go wrong and it is well built (engraved, too) It also has strap lugs