Garry,
I seem to remember that this particular pagoda has the 2 piece metal breather line which is correct for your August 1965 built date.
The only way to check is to remove the entire assembly from the engine.
To remove the hollow bolt and banjo fitting on the valve cover, you need a 24mm hex socket or spanner.
Once removed and the two pipes separated from the rubber joining hose, you can blow through the pipes with your mouth.
That is about the simplest test you can perform.
Most of the time, these lines tend to rust from the inside out and get blocked even though they appear fine from the outside (think atherosclerosis...
)
Rather replace than to try and unblock.
I had a similar problem and ended up taking both metal lines to a pipe/hydraulic shop. What they did was to bend new pipe using the old ones as a template
and they then soldered the old banjo fitting back on.