Aimee, I'm not quite old enough to have built many houses in 1947 but I did watch the carpenters finish building our sub in 1954. The dimensions then were the same as they are today except that x8 did tend to run more like 7-1/2 than 7-1/4. Same for the x10 and x12's. There was more variability in the sizes then because the mills were not as automated as they are today.
I have worked a saw mill with some sawyers that fought in the Spanish-American War so I guess that you could call them old-timers. They all sawed to 2 sizes, planks and boards. Planks were sawed to a little over 2" and boards were sawed to a little over 1". After drying and planing, these would finish at 1-1/2" and 3/4" respectively.
My daughter has a 160 year old farm house. Some of the wood was sawed on a water powered mill. The 2x's were used without planing (and probably not much drying either) but still measure right on 2".
This is not to say for sure that your boards are not 8" but this would be pretty unusual. What do they actually measure?