Smoke from breathers.

I have beat on my 340 for 18+ years and its getting retired for a 408. only because it smokes a little in the shut down area.(probably valve guide)
But, my point is, that the only time i get smoke to come out of my breather is when i disconnect my pcv from the valve cover.

Are you Positive that its working properly? Does the hose from the carb have vacuum? could it be plugged/restricted?
Pcv not fitting tight in its grommet?
leaking around the carb to hose/ hose to pcv fitting?

Your finger and some carb spray is all you need to do these tests..............