in my 1984 4.2 I have used Splitfire plugs with a lot of satisfaction. Then I tried Bosch Platinum with the 4 tips, and they have been a total dissapointment. With the Splitfires the engine started from "touching" the ignition switch, with the Bosch plugs the engine takes some cranking to start it and also misfires at idling, which it didn't do with Splitfires.
No more Bosch, and I wouldn't throw my money away on Champions or anything like that. NGK ? I never liked them either, lots of hype, no substance. As long as you have the correct plug tip setting, no other adjustments should be needed. I'm sure other people have had different experiences with similar plugs. I'm going back to Splitfires.