I did a search and read some of the threads on this. Is anyone running their Cats with any lead additives? I have a 69 with a recently rebuilt, slightly modified 351W. I do not know if it has hardened valves or seats in it. I am running 91 octane now and the car is not a daily driver. I have had it on the interstate and freeway doing 65 MPH (or more wink). Does it make sense to put in a lead additive to a tank of unleaded gas as a preventative measure?
My 69 has a similar story, recently rebuilt engine and lightly modified.
The previous owner told me he used unleaded as it had been rebuilt using hardened valves etc.
I can’t imagine any engine being rebuilt in recent years and not having been updated like this.
I also would have thought that if you not using it as a daily it would be fine anyway.
I’m no engine expert though so I may be proved wrong 
I don’t use the lead additive, but do use the ethanol treatment.
Lead in gasoline protects the valves and valve seats from wear. Your engine will run fine without it for quite a while. It (your engine) will wear out faster without lead. Hardened valve seats and stainless valves do not wear out as fast as standard valves and seats do. This means you can run without lead in engines that are set up this way.
I had one 390 engine with a valve that was recessed into the head almost 1/4 inch due to wear from no lead. I have modified all my engines to have hardened seats. I do this when the engine need machine shop work anyway. I used lead additive in engines that have not been upgraded.
In your case, you need to decide if the cost and hassle of using a lead additive in every tank of gas is worth extending the life of your engine’s heads and valves.
I buy about 6 or so bottles of additive in the spring and put maybe a half a bottle in when I fill up. This gets me almost though the summer. I look at this way, it’s not that costly, it’s always in my trunk, so pour some in. My understanding from previous owners is that my 302 has never been rebuilt and the odometer rolled over 200,000 miles last fall.