I did not realize that the distributor in my car was not a 57, but an early one with no mechanical advance.  ( loadomatic ? ).  Today I installed a  real 57 distributor with vacuum and mechanical advance and it is running much better.   Our summers are very short in Mass. so I'm going to drive the car for now and wait until about September to tear down the rear WCFB and plug that hole as you suggested.    You are a real help to guys on this site.   Jay