The cars that suffer from today's unleaded gas, are the high compression models from 1955 to 1970. After 1970 they were made to use unleaded.
A quick rule of thumb is, the octane should look like the compression ratio. So, if your compression is 8.7:1 or less, you will be fine with today's 87 octane regular. If your compression is 9.2:1 use 92 octane Super.
This is not an exact rule, just a guide. But if your compression ratio is 9.5 or higher you may need water injection or octane boost additive.
Some old car owners add kerosene or diesel fuel to the gas to LOWER the octane. They find their cars start easier, run smoother and cooler, and develop more power on a heavier fuel. This only applies to really low compression cars from the twenties and thirties, with 4:1 to 6:1 compression.
In any case, you can always add some Redex, Bardahl or your favorite upper cylinder oil to the gas. Even a shot of 2 stroke oil to lubricate the valves. It can't hurt .