You won't need to change your oil fill/breather cap; the same one was used with the road draft tube and with '61-'64 (California) '61-'68 (rest of the states + Canada) PCV systems.
If your carburetor has a big vacuum port at the base (presumably it's capped right now), then it's already calibrated to account for airflow from the PCV valve.
Remove the road draft tube, install a PCV cap and valve, run a length of appropriately oilproof hose from the PCV valve to the carburetor port, readjust your idle mixture and speed, and you're all set. The PCV cap you'd need to keep using your pre-'66 valve cover looks like a roughly 2" diameter metal version of an aerosol spray can cap, with a hole in the middle, and it uses a 2-legged steel spring to hold it firmly to the valve cover chimney.
Here's a new one.
Picking a PCV valve requires some caution; many different valves will fit and look alike, but they have different flow characteristics and spring calibrations. The 170 engine takes a different valve than all the larger engines.
The original '61-'63 valves were a metal item made by AC and designed to be taken apart for cleaning. I might still have one or two of those new in box (and the separate metal elbow they take); ping me if you want me to check.
If you don't want to mess with hunting up obsolete parts and you'd prefer to shop for a current-production PCV valve, the one you want is Standard №
V253. These currently-available PCV valves are a different style, made partly or completely out of plastic, and require some adaptation to use with the pre-'66 valve cover and PCV cap. You make a sandwich in this order: PCV valve (push the non-hose end through the cap from outside to inside), spring retainer,
grommet (push onto non-hose end of PCV valve from the bottom). Sometimes the spring retainer won't fit over the plastic valve and you have to leave it off. Push this "sandwich" onto the valve cover chimney. It won't look quite original, but it'll fit and work fine:
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