Marvel mystery oil used as a lead substitute?

I have used MMO in several vehicles for years. I can't attest to benefits from tear downs but . . .
I had 79 258 6 in a CJ that was rebuilt stock but had balanced and ran a 1/2 quart in crankcase at 3000 mile oil changes and recommended mix in gas tank and that puppy ran like a Singer sewing machine. Naturally it was hardened valves, I'm thinking it couldn't hurt ?

It is more than a capful per tank, I don't recall but seems more like 3-4 Oz per 10 gallons.