I have researched the numerous postings on pcv valve systems, and have been amazed at the creativity of the individuals on the Forum.  My question relates to the choice of vacuum sources to attach to the valve.  The most popular source seems to be the plate that fits under the carb. with an attached vacuum connection (CASCO product).     
The '57 Tbird I recently acquired has the vacuum hose connected to the fitting at the back of the intake manifold where other vacuum sources are connected (power brake, vacuum advance, fuel pump).  A previous post indicated that the rear manifold was not a good place to use because it would cause the rear cylinders to run lean.  Is that really a concern, as the other vacuum sources are already attached there.  Does the pcv draw more air than the other components, and possibly cause a lean setting on some cylinders? 
Thanks, Ralph