They used the same diagram in the 1970 Chevelle Assembly manual for the L78 Chevelle.That "Smog Tree" configuration was offered in two designs for the Solid lifter Chevelle.Early versions (Dec./Jan.) received the "Hockey stick" design,with later(Jan./Feb.) getting the design where the valve was connected in the lower middle of the Valve cover,which appears to be wthe design your diagram shows.
I hope you can find those Dual Snorkle PCV Rare clips,and share a picture with us.
