Are you interested in a static shear strength (yield or ultimate load case) or a dynamic strength (fatigue)? 1074 is almost always used in spring applications, so I am not exactly sure what you mean by "shear strength allowable".
And/or if you have the tensile allowable then the shear allowable will be about 1/sqrt(3) times the tensile allowable (about 0.57x) based on Vonmises criteria.