You are right about the Chrysler engines! Back in the late 80s, my boss had a 42 Dodge Sedan, we painted OD with white stars. It had a bad rod knock at anything over 40 mph. He was a great boss, but put a whole new meaning to the word cheap. We pulled the oil pan and did the old emery paper and new bearings dodge! The car ran great, and was still running a decade latter after he passed away! I wonder if it just might still be running with that fix?It is a myth that old engines need non detergent single weight oil. Multigrade detergent oil has been available since 1951 and was the default choice in every garage and dealership in the fifties and sixties. So chances are any car made after 1950 has never used anything else.
I worked in a garage in the sixties and did many oil changes. Practically all of them with 10W30. We kept 30 non detergent bulk oil for cheapskates with old oil burning klunkers but they never changed their oil. Just poured more in when the crankcase was low and bought $2 worth of gas.
Chrysler flatheads are well behaved engines and hardly ever make bad noises or show signs of distress even when badly worn. They just get slower and harder to start.
I think the mechanics were astonished when they took Lizzie's engine apart, that it even ran. I know other cases with similar engines that were rebuilt and the owners were surprised by the new found power. They didn't know how bad the engine was because it gave very little sign. I know one guy with a 41 Plymouth coupe who wanted to change the rear axle ratio or install a 4 speed until he had the engine rebuilt, the new found power took away all need to make other changes.
If your oil pressure is low and your compression is low you should think about doing something about it. But if you choose not to, it may run a long time if you baby it as I said before.