360 Aftermarket Heads on 318

Typically, with iron heads, and on the street, the limits are; 165psi for 91gas, 160 for 89, 155 for 87octane.
Closed-chamber heads running a tight Quench, may go a lil higher.

You can go much higher than that. There's more to detonation than just octane ratings. That said you need to pay attention to the details to make it happen. Would you run 11-1 comp with a 218 @ 0.050 hydraulic cam?