Max cyln pressure on pump gas ?

In my opinion that builder that dropped 120psi with a cam only ended up with one heck of a turd as an engine. Can it be done? Probably.. But you're talking about an engine that had a cam that was in the .500+ lift range with a high static ratio going to something like .650 lift with a wider lobe seperation angle...lol. It's the wrong approach.
My "guides" for various combos on pump mid grade (89 octane, 10% ethanol) are these:
Iron head - open chamber - no quench - max dynamic of 8.25:1
Iron head - closed chamber - with quench tighter than .040 - max dynamic of 8.5:1
Aluminum head - closed chamber - with quench tighter than .040 - max dynamic 8.75:1.
There's not much difference, but there is some. Also because dynamic compression ratio is calculated with 100% filling of the cylinder and cylinder filling on a good engine will exceed 100% before peak torque is reached - the cylinder pressure will rise with rpm to a point. You can be fine on pump swill with 9:1 dynamic while tooling around at 3K rpm. But when you hammer down and run it up to 6500, it more than likely is detonating whether you can hear it or not. So I build for lower dynamic. As long as you design it into the build there is no real compromise or drop in power from it.