What Year Valve Cover?

Finding a good-quality(!) oil cap/breather for the pre-'70 covers is more difficult than dealing with the PCV system.

With a '66-'69 valve cover (one chimney, one flat hole) with a factory grommet you can use a factory '64-'69 metal curved-pipe PCV valve if you want the old-school look (and a valve that's never going to object to occasional dosing with carb cleaner). These valves are growing scarce and costly on the open market, but I have a stash of them; send me a PM if you want one. Or you can use a '70-'71 style plastic/metal valve, or a '72-up all-plastic valve. You can even use the AC-style take-apart valve if for some strange reason you want to. All of these options are extensively discussed and pictured here.