A friend of mine (who lives on a farm) bought a Massey Fergusen combine that was made in 1974. This thing is powered by a Chrysler Slant-6 (225 cid) engine.
My first car (which was at the time a 20-year-old 1965 Dodge Polara) had a slant-6 and I rebuilt it once or twice during the 10 years that it was my daily driver.
I know that the theory was that leaded gas helped lubricate the valve seats, and unless you did a valve job and had the valve seats hardened, that the use of unleaded was supposed to wear out the valve seats on these engines.
So I'm wondering if anyone knows if a 1974-vintage slant-6 could run on unleaded gas (or what-ever passes for gasoline today).
I looked through the manual for this combine - and it says absolutely nothing about the recommended gasoline - not even the octane.
I seem to recall that in the 1990's that you could get a can of additive to throw into your tank to substitute for leaded gas - I have no idea if that stuff is still available.