Dunno if it's any help to you, but I fly the ONLY American Turbo-Prop ever to fly in the era you refer to. The L-188 Electra was, sadly for Lockheed, built at the same time as the B-707 and therefore, sadly, mostly suffered the same fate as the Viscounts, Vanguards, Argosys etc etc. However, as a proud Brit, I do find it irksome, much as I love the Electra, that ALL the wide British variety of turboprops are history, and yet the Electra, the ONLY American turbo-prop, continues to fly all over the place.