The stock setup has a PCV valve in a grommet in the driver's side valve cover, and there is a large diameter (3/8"?) rubber line running over the the carburetor. This is where is is sucking crankcase vapor into the carb base and then into the cylinder. As someone else mentioned, adding this extra air source may make your carb go leaner.
On the passenger side you can use a vented cap in the valve cover or a rubber line running up to the air cleaner filter area (this is the stock arrangement). This is where ambient air is sucked into the crankcase, so you just need a relatively clean air path. The stock setup uses a rough mesh filter on the air cleaner fitting to prevent sucking in too much dirt.