The octanes available in the 40s were much lower than anything available now - so don't sweat that. If its a 40, it should be a BE engine as opposed to the later CE engines. It could have even been set up for Kerosene/Distillate - look for a K suffix on the motor S/N as opposed to a G suffix. Motor s/n is most likely steel stamped into edge of left side of motor flange where it mounts to transmission. Even the late (1950's) CE engines should have no issues with octane.
As to alcohol - I have to disagree with those that say its not a problem. It can be dealt with, but anything rubber in the fuel system may be a problem. I have had fuel sediment bowl gasket swelling problems as well as valve packing problems. And yes, I verified it was alcohol related. Put a new old stock rubber gasket in gas for 2 days - no change. Put same gasket in gasahol and it swelled significantly overnight.
Other significant issue with all fuels is long term storage - issue is more severe with alcohol - read the instruction manual on your ATV or Lawn Mower or Boat Motor. The more recent ones are more tolerant, but they still have issues. Water absorption is less of an issue in dryer climates, but in high humidity or significant temperature changes, you can have condensation & rust. Seafoam is one additive I use in my ATV when I can not get Alcohol free gas, there are others at Walmart or Home Depot.