"Are there anything that indicates rockers before or after 1959?"

The position of the oil groove inside the rocker arm is the best way to identify the early or late design rocker arms. The later model part that was used with full oil pressure to the rocker shaft has a groove that's offset from the spit hole in the top of the rocker. Earlier models that used lower pressure inside the rocker shaft have the groove aligned with the hole. The shafts are the same design for about 30-something years of production, from the 1940's to the early 1960's.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!