No I have not. I was just giving my real world experience having put over a million miles on MOPAR engines in answer to "Synthetic oils are the only oils to use". Most of my engines have been in service for 30 to 40 years long before synthetics were available. Most have between 250,000 to 300,000 miles on them. They all still run like new having run Valvoline Racing oil. You all can drink the "cool aid" if you want. From my experience with engines from the 2.0 liter 4 cylinder, to a 4.0 liter Jeep, to high winding 273's, to a 383 synthetic oil is not "needed". Carry on with your theoretical "better" oil discussion, keeping in mind the OP is running a tired 74 slant six. He absolutely does not "need" synthetic oil.
