Have you rechecked your valve lash? V6s are solid cams.
What's your fuel supply like do you have pressure and flow?
The Stromberg WW has idle screws circuit screws and internal tubes that feed that circuit what happens when you turn those screws does the RPM or vacuum change?
https://www.carburetor-blog.com/know...e/ww-exploded/
Here is some more info on the WW carb
https://www.carburetor-blog.com/article-categories/ww/
BTW that is a breather in your valve cover that goes to the air cleaner it won't cause a vacuum leak.
https://6066gmcclub.com/showthread.php?t=48799
The PCV valves screw into the head on V6s
GM part number 6421979
AC Delco CV623C
Good luck and keep us posted