What it will do is : cause your engine to explode so you'd best remove it carefully and mail it to _me_ for proper disposal....
Yeah , right !

the PCV valve proper is the black rusty cylinder screwed into the brass elbow sticking out of the breather , soak it well to clean it out , don't be worried at the amazing amout of toxic waste that drains out of it . a PCV system keep the inside ofyour engine clean and a clean engine is a happy engine that loasts longer and rund better too .
You should consider cleaning out that big old breather tube too ~ it's full of baffles and sludge ~ remove it and send SWMBO & the kids off for the day , drag out your old charcoal BBQ and stoke it to red hot , lay the breather tube on the grill and close the lid , let if cook for a few hours , it'll begin to smoke & stink something fierce so be _sure_ SWMBO isn't going to come home soon ! . once cooled down , tap it to shake out all the burned ash , DO NOT
EVER bead blast a breather ! .
I notice you have a " Dual Action " typ fuel pump ~ this is a great find , what it is , is this : a vacuum pump built into the lower half of your fuel pump , it will ensure your vacuum wipers run perfectly at all speeds and loads ~ obviously someone liked this truck and equipped it properly ....
Engine idling , test for vacuum at each of the ports on the bottom half of the fuel pump . you'll be wanting to connect this and I'll tell you hoew if it still works . if not , don't panic , just mail it off to a vintage fuel pump rebuilder .