[AZKen]

This item is confusing because our own "known good parts" shows both types for the same year motors. Rockauto shows window up to 65-66.
Jolly shows two types of caps and two types of vac advance depending on the distributor weight design as Pete says. Parts are shown for same years 63-66. As Pete says, some motor had one way and some another.
This may conflict a little with Pete and I am not an expert but, sounds like early (60-62) caps were known as small cap and has clips to hold the cap on. Also the rotor was slip on with weights under plate. 63-65 sometimes called "large" cap and have "L" pins holding cap on, under rotor weights and screw on rotor. The cap had a window. I said confusing, right?
As far as I can tell the answer to the question is no window 60-62, window 63-65, no window 66-up.

I don't know if there was a clip-on cap for 305 V6 or not. Sometimes the I6 stuff gets confused with V6 stuff. BUT: The Chevy I6 in 60-62 had a clip-on cap. No window in I6, window in V8's. Then in 63 went to "L" pin.