I know you can go a lot higher than that, I'm basing it on what I know about the motor. The only thing I don't know in calculating the comp ratio is head gasket thickness, and exact deck, but I know it's right around zero deck.
I have more information. The engine is stock bore, stock stroke, stock pistons and stock deck. It has j heads with 2.02 valves and 3-angle valves. Why on earth would this thing be running 100 octane? Shouldn't it be 8.5-1 compression it's a 73.