Along with what you already found with the distributor, the bushings can and do wear which will cause misfires, and reduce fuel economy and performance. Check with your local auto parts store for the price and availibility of a remanufactured or new distributor, (stay away from rebuilts). You'll be pleasantly surprised at the price difference compared to the MSD too. As far as the distributor cap, rotor, and spark plugs, use AC Delco ONLY on the 4.3L engine. When it comes to spark plug wires, Autolite Professional Series have the best specifications of any manufacturer, and at a lower cost too. Unless the ignition coil fails the resistance tests, it should be fine. Standard OEM coils are more than adequate to do the job. Provided the cap, rotor, plugs and wires are good, "High performance" coils serve no purpose other than drain your wallet.