Jim, please clarify on the following:

1. The original 400 engine has a stock rebuild meaning original pistons, heads, intake, carb, exhaust.....
Are these Pontiac pistons on standard bore, or aftermarket pistons on .030" over, etc.? Cast or forged? What cam? How is it degreed? What brand, composition, and compressed thickness of head gasket?

2. So, it's running 10.75 to one compression.
Is that calculated with all the engine build details, or simply relying on the advertised figure Pontiac used, which has no basis in reality? Do you have your cylinder cranking pressure reading?

This is simply to get a better idea of the details of your baseline. Mine is the original unrebuilt '69 400 with 76K miles, steel shim head gaskets, the whole shot. The only changes are the timing set and a Pertronix Ignitor II in place of the points.

If you take 12 gallons 93 octane and 5 gallons 110 octane, that gives you 98, but close enough anyhow. Our cars were rated for 100 octane so the minor changes you've made should make that bleand palatable.

I've been running Max Lead for 2 years, one quart per tankful. It helps, but my car has more power and runs cooler and permits more advance on a 50/50 blend of Turbo Blue 110 Leaded + Super Unleaded 93 without a doubt. If the leaded fuel was regularly available close by I would not use the Max Lead at all, but it's good to be able to carry a bottle in the trunk in case I am away from good fuel.