Ralph,
It doesn't seem to me that removing that small vacuum line to the advance can should affect your engine as much as you say it does. If the engine were experiencing a partial vacuum leak somewhere, and you jiggled that hose and added another leak, then what you describe makes sense.
I would take a can of Brake-Kleen, or a propane torch (not lit) and go hunting for vacuum leaks. Small blocks are notorious for developing leaks where the intake mates to the heads. Good luck.
Stuart
