Depending on where you live you may be able to get non oxigenated gas, we have a lot of old car guys around here, lots of muscle cars, those organizations do a great job of pressuring the legislature to have non ox available, it costs a little more but if your worried at all its a good alternative.
These engines were designed for a very low octane originally. Around 68 octane, I believe. You definitely don't need to use premium fuel. Regular unleaded will work fine. These days most fuel has ethanol mixed in and that is becoming a problem with the older engines. The rubber parts in the old fuel systems are being eaten up by the ethanol. But until that happens, it runs fine in these engines.
Most folks say that you don't need additive for your valves unless you run the engine hard. I have had an M-38 since the early 70s and never run anything but unleaded regular in it. It gets probably only around 500 miles per year or less and runs beautifully. Other than regular maintenance it's never been worked on.
