In Continental powerplants certificated for, and approved for 96 octane, 100LL, 100/130, and 115/145 fuel are also approved. That includes the IO-550. See the previously referenced document.
The Type Certificate Data Sheet for the IO-550 lists 100LL, B95/130 CIS, or RH95/130. The document cited previously provides that all Continental powerplants certified for 91/96 or 100/130 may also be run on 100LL or 115/145.