Lycoming has already signed off that G100UL is an acceptable fuel for all of their avgas powered engines. Continental has done so as well. Interesting point about European plane builders; Pipistrel originally designed their new Pahthera to use the Lycoming IO390 engine, but later switched to the IO540 instead. One reason why is that the 390 requires 100 octane fuel while the 540 can use the 94 octane unleaded mogas.