I was advised to run the VW in my Turbulent on a mixture of Avgas and Mogas, to replace the lead that used to be in Mogas, but is now unleaded, never had any problem. There was a specific ratio which I can't just quote, but about 25% Avgas if I recall.
I initially ran it on Avgas only - after all, it's an aeroplane, isn't it ? - but then realised that the engine was a cooking standard 1200 cc Beetle, designed to run on the cheapest petrol, so why waste money, but eventually settled on premium petrol with a dash of Avgas.