The PCV valve on a 261 engine was screwed into the fitting that comes off the oil separator tube (the tube that replaced the road draft tube in PCV-equipped trucks).
You can see the PCV valve in this photo - it has the hose clamped to the top and it and it is threaded in the bottom. The PCV valve can be removed, taken apart, and cleaned. There is a photo of the expanded PCV valve-parts in the Shop Manual.
http://i115.photobucket.com/albums/n282/spdzrus/connecttometaltube.jpg Do you have a tube going from the air cleaner into the valve cover (allows filtered air to be drawn into the valve cover)?
