How do you know if your vintage car needs valve seats?
Brand spanking new or vintage car; the procedure for diagnosing bad valve seats is the same.
You run a dry and then wet compression test on all cylinders. If both the wet and dry test shows low compression in that cylinder, the valve seats are likely not sealing.
A leakdown test will also show bad valve seats but you need to listen at the exhaust and intake for the “hiss” of leaking valves.
If your engine is running smoothly and easy to start, you don’t need valve seats. If you are worried about unleaded gas, I used to run Amoco High Test unleaded in the 60s all the time and it had no lead. There are also lead substitutes in a bottle. Unless you are using this as a daily driver I wouldn’t worry about it.