The statement "Climb at 64 mph for best angle" does mean Vx. The POHs for those years do not specify on one page like the lattest models all the V speeds. V speeds existed then as they do now.
The Cessna manuals have evolved over there years and now provide more information than early 70s manuals.
The term POH is not a requirement in any Cessna because a Pilot Operating Handbook is not an AFM (Airplane Flight Manual). If a Cessna manual is required for a certain year it would be the AFM not POH. A POH is a reproduction of information from a AFM and is for pilot infromation only. It is not an FAA approved AFM.
Also the O in ARROW stands for Operating Limitaions only not "operating handbook/limitations".