JMHO, 3lbs free flow may be correct for a pump that puts out 10lb static pressure. And, 3lbs free flow (constant at the carb) may not be a problem for a carburetor as long as the flow rate keeps up with demand (pump can maintain 3lbs or close to it at sustained WOT). Carburetors depend more on flow (volume) than pressure.
Your sputtering at low speeds could be carburetor related, as in the idle restrictor too lean or gummed up, which will effect the transition circuit and cause sputter. Try cleaning the idle fuel and air passages. Also take a look at your plugs to see what the idle/transition mixture looks like it may need to be adjusted.
MSD or any type of multi spark ignition requires REALLY GOOD POWER and GROUND connections, these should be sourced directly from the battery. Many failures can be attributed to incorrect wiring practices. Further complications with multi spark ignitions can be caused by incorrect spark plug wires (too low of impedance) and believe it or not the cylinder heads not grounding well, a separate ground wire to each head is preferred with multi spark. And always disconnect the MSD's power, ground and tach wires when welding on the car.
"It seems nothing can last nowadays anymore." We are starting to sound like our fathers, lol!