I will be rebuilding my first Pontiac motor, a 68 400. I've done several Chevy's but am not familiar with the Pontiacs.

The stock compression ratio is supposed to be 10.75:1. I would like to reduce it to around 10:1 by using different pistons.

Are the factory pistons flat topped? If they are, do they make dished pistons?

Should I even worry? The customer uses premium anyway and doesn't have a problem with that. But, at the moment, the cranking cylinder pressure is very low, about 50 PSI and I am worried with a fresh rebuild the pressures will be too high. I am also planning on using a new cam with the factory grind. Is today's 91 octane enough for this motor?