How does this 360 Magnum combo sound?

It's the dynamic compression ratio that determines octane need. That is a calculation that takes inot account the closing event of the intake valev, and the rod length. You want to run at max 8.25:1 dynamic for good power and no issues with 86 octane with iron heads. If you go aluminum, you can bump that up to 8.6:1 dynamic. If you need power brakes (vacuum), you'll want to build using the aluminum heads and a lower static ratio with a smaller cam. That will be all torque. Also bear in mind, hydraulic roller cams are different, and I would stay hyd roller in this build.