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I have the above tractor a 1949 4 cylinder gas motor. I've been running 87 octane gas in it and my question is, should I be adding a lead additive to the gas? Never thought about it before, everything seems to be running fine. Just wondering, opinions?

Newer motors have hardened valve seats which accommodate unleaded fuel better BUT I really don't think that'll be an issue unless you're "killing-it"
Your main concern should be rubber gaskets and hoses in the fuel system.
Rubber doesn't react well to ethanol and other additives in today's 87 octane, it dissolves.
Fix is simple, replace rubber components with neoprene equivalent and use fuel stabilizer such as SeaFoam.
For the record... Shell 91 is guaranteed ethanol free.

Valve recession is mainly a problem in high revving applications, according to most literature. I read some SAE papers on this topic in the 80's while working for a car company. Your tractor is low revving, probably OK.

The car company that I worked for sold an engine designed for unleaded fuel in the Canadian market where lead was still allowed. The lead wrecked the oil rings, leading to oil consumption. Owners didn't check their oil and ran the engines dry. I saw scores of returned wrecked engines. Most engines designed for no lead can run leaded gas fine (not the catalytic converters) but this engine was an exception.

In your shoes I would run 91 ethanol free with a lead substitute additive. As close to design intent as possible because there could be a weakness there.

Lead is an octane booster, it prevents premature ignition (knock) in unstable fuel.

Valve seats, among other things, are damaged if engine knocking occurs. However, it takes prolonged engine knock to damage the valve seats, the bearings are the canary.
If you reduce or eliminate the engine knock, you reduce or eliminate the damage to the engine. Including valve seats.
The lead it self provides no other significant effect beyond stabilizing the gasoline.

As long as no engine knock is occurring, you're fine.

Alcohol has been said to cause issue with some fuel system components, such as rubber. But who knows, could be a load of hoey put forth to make money off telling fibs.
Run Shell 91 like those guys are saying.

The internet says.
Lead does cause spark plug fouling, problems with catalytic converters, brain damage, etc.

Knock is not what causes valve seat recession. I wonder if I have any SAE papers left...

Knock is not what causes valve seat recession? Refer to SAE paper 860090 - you really could buy a copy on line from the SAE

Heat causes valve seat recession. Heat is far greater in an engine that is knocking, then in one that isn't.
I'm just saying that lead doesn't do anything other then to control heat and or detonation.
The fuel available at the pumps in Canada is good enough for preventing detonation in most engines, except those with very high compression or higher heat.
That's all.

I got unnecessarily wordy. Sorry about that.

I think lead is still used in gasoline in a number of countries.

The removal of lead was a big deal. Engines had to have hardened valve seats added or have induction hardening of the valve seats. From the SAE paper I mentioned above:


Lead compounds, formed by the combustion of lead anti knock additives, prevent valve seat recession by forming a thin non-metallic layer of lead oxides and sulphate son the surface of the valve seat. This acts as a solid lubricant....

I am not much of a mechanic but I read a lot

I would be installing the Edelbrock etc additive to the oil as the new passenger car oils are blended to be catiltilic converter and O2 sensor friendly and are missing the magnesium and other additives that provided cam lobe lubrication in the older oils, this is why all the newer cars are hydrallic roller cams witch require less lubrication. I got burned years ago with a solid cam in my race car when this issue was just being discovered.

Oil is another key thing for old engines. Old engines need ZDDP. The best oil I have found for my Lotus is Joe Gibb's Hot Rod Oil, synthetic. I say that based on maintaining oil pressure when the engine overheats. Gibb's is better for that than Mobil One or any of the other oils I have used.