I have 89 octane ethanol free gas available. I Need 91 octane for the 912 ULS. I am thinking of mixing 100LL and the ethanol free gas, along with decalin, to get close to 91 octane. That way I get less lead, and no Ethanol, but still get the required octane. Anyone know how much 100LL I need to add to the the 89 octane gas?