They were likely referring to the fact that the leaded gas had a higher octane rating. The hot V8s of the same era had to be de-tuned to run on the unleaded stuff. Usually reducing the spark advance curve, using a cooler thermostat and fattening up the carb jetting would get some of the engines by on the high-test unleaded. But its a stopgap measure, cuz the V8 engines with over 10:1 CR will still detonate even with band-aid tuning tricks.
On a 235 its unneeded as the compression wasn't high enough to cause detonation anyway. None of the 235s had induction hardened valveseats, cuz they went out of production 10 years before unleaded gasoline. Any high-mile 235 will show SOME valveseat recession if its been used regularly onroad after the advent of unleaded.
My 235 had terrible seat damage, and some exhasut valve warpage due to this. My car saw many hard miles on unleaded gas. Had to have my head reworked when I did the engine the first time. Now the head is the only part of my 235 currently together. *G*
