I can't provide any scientific support, but I have been adding lead additive to the tank of my 54 3100 with the original 235 engine and I can tell the difference. No change in performance, but I can tell you it quiets the engine down. I have engine knocking at start up and certain stages of acceleration running through the gears getting to cruising speed. The knocking is predominately more noticeable and more frequent without the additive. For 2-3 dollars a tank full, I will keep adding it. For those of you old enough to remember the gas commercials before unleaded gas, I can't remember which gas company but one of them would promote their anti-knock formula as a reason to buy their gasoline. Here is a link to the history of gasoline and they talk about lead as an anti-knock additive.
http://www.petroleumhistory.org/OilHistory/pages/knock.html
