Old cars break stuff, it's a fact of life. Sometimes, however, it's not obvious that something's broke. It's more subtle.
Hard starting, a loss of power or just that feeling like you're dragging an anchor behind you. You'll get where you're going but it won't be as much fun getting there.
When everything else has been checked and you've got symptoms like the ones above it might be worth a look at your vacuum advance unit on your distributor.
Most points and early HEI ( non computer controlled) units will have them and when they go bad you usually don't get any notice.
There's two easy tests that don't involve anything but pulling the vacuum hose off the carburetor (because chances are you don't have fuel injection) and see what happens.
Get the engine to operating temperature and then pop the hose off the vacuum advance unit. If the idle speed drops you know the unit is probably good. If nothing happens it's probably bad.
Time for the next test.
Get a vacuum pump like a mighty vac hooked up to the vacuum advance unit and give a few squeezes. Whether the engine is running or not, you should see some vacuum reading on the pump's vacuum gauge. If the engine is running you may hear the engine speed up as well.
If you don't get either of those things and you know the pump is hooked up and working right then you've got a bad vacuum advance.
Trolling the automotive forums most people will tell you it's an easy fix. You pop the distributor cap, remove a couple of bolts and wiggle the old one free. Of course it gets more complicated if your distributor is hard to access and it's even worse when the engine is hot. Yeah, you can probably change it in 5 minutes if you yanked the distributor out but that's usually an even bigger pain than dealing with it in the car if your setup is anything like mine.
I made the video below because nobody was ever going to read the 1000 words it would take to describe a 15 minute job.
So have at it and check off another little project on your classic car "to-do" list.