Greetings. I'm looking for direction or a clue as to how I could find the prevailing compressive strength, f'm, of CMU during the 1940's and 1950's ... I'm greatfull for any help that can be given.
They are very low values, but in the absence of better information, you might consider using the default values of Chapter 7 of FEMA 356. They are 300 psi for poor condition, 600 psi for fair condition, and 900 psi for good condition. These are said to be lower bound values, and you can multiply these by a factor of 1.3 to arrive at the expected strength value for each respective condition.
I can give you the average tested value of brick 250 yr old tested at Zaragoza, Spain exposed to severe wind erosion (some limestone inset sculptures completely eroded windwards) and mist in winters: 90 kgf/cm2 for yellow brick, and 138 kgf/cm2 for redder brick. Taken with gypsum mortar, the limit strength of the masonry in compression for the standing spanish code was estimated to be 19 kgf/cm2 (9.5 kgf/cm2 allowable with SF=2). Tensile strength of the masonry was estimated 10% of the compression value. Amplifications due to buckling if any to be considered when checking against the corresponding limit.