Check for vacuum leaks at the carburetor joints and at the base/manifold connection. Rochesters have a tenedency to warp and suck air. Check for vacuum leaks at that gasket you're thinking about replacing. Vacuum leaks can cause poor idle situations.
The vacuum line that's plugged on the intake manifold is for the windshield wipers. Make sure it isn't leaking.
After you fix everything, shop around for the correct Carter YF carburetor and rebuild it. You will never look back after ditching the Rochester.
Is there some particular reason you want to replace just the spark plug wire boots and not the entire wire(s)? If the boots have been on long enough to deteriorate, it's time for new wires.
