"Are octane ratings from the 1940s directly comparable to modern ones?"
Yes. The equipment used to determine the ratings was designed in the '30s and '40s. The same basic designs are used worldwide today. Only one manufacturer is authorised, Waukesha. There are Russian copies I believe but I've never seen one.
100LL and 100/130 is essentially the same spec and can be interchanged. The only difference is 100LL has Low Lead, ie. less TEL added made possible by using higher octane blendstock to achieve the same octane performance i.e. 100/130.
The 100 bit refers to minimum 100 MON (usually around 103-104 MON on the stuff I tested) while the 130 refers to minimum Performance Number of the fuel tested on a supercharged version of the MON engine (usually around 132-132 P.N.)