In addition to the above, the STC requires that automotive gas with 0% ethanol be used. In many parts of the country, that is extremely difficult to find. In my area, the only place to buy it is one farm co-op that is way out in the country. In some places, it is not available at all. Luckily there's a website to find it, but places that carry it have been getting fewer and fewer. So the MoGas STC is not a long-term 100LL workaround.

https://www.pure-gas.org/