A lot of misinformation here.
L79 was an engine option that required certain transmission and differentials (12 bolt and option of heavy duty 3 speed or 4 speed).
L79 could be ordered in any Chevelle/El Camino.
Tachometer was a separate option.
SS was a separate option.
Z16 was a package with a long list of required pieces. They were built and people had the option to buy or not.
(375HP 396, 4 speed, 12 bolt, AM/FM stereo multiplex, boxed frame, larger front and rear drum brakes adapted from full size Chevrolet. Unique rear trim package, rear sway bar, and probably some things I have forgotten.)
1965 was the first year for VIN stamp on engine block, L79 and Z16 only. The L79 stamps were not gang stamp, individually stamped and not very straight.