Since your bow was likely made in the early sixties, I would guess that it is not cut to center. "Cut to center" is referring to the distance between the centerline of the bow and the strike plate on the side of the sight window. The closer the plate is to center, or even less than center, the stiffer the arrow that the bow will shoot well, the "archers paradox" being not so severe.
Another thing that would influence spine would be the actual physical (mass) weight of your arrows. Laminated arrows, and those made of hardwoods like ash are heavier than those made of spruce or cedar. This slows the arrow down, and necessitates a lower spined arrow to compensate.
My choice regardless of the weight, however, would be the 40-45# spined arrows. I am going by the type of bow and your draw length for this conclusion. The aluminum arrow that I would use is a 1916 with a 125 grain head, or a 2013 with a 140+ grain head.
Hope this helps,
Killdeer