91 Octane in a 340?

Im wondering if I can run 91 octane, so far I've just been running 94 but it's expensive and harder to find in my area. The engine is mostly stock from what I understand, so 10.5: 1 pistons pre 1971 with X heads. Though im not sure of the cam but I believe it's a COMP XE284 high lift but might be XE268 aswell. I have a Edelbrock AVS2 800 Carb I believe aswell. I just checked the timing and its set at about 33 degrees @2500RPM. The cam definitely has more duration than stock though and it's lumpy at idle. Would a cam with a longer duration bleed off more cylinder pressure and allow advanced timing or lower octane gas, or am I not understanding something?

Given the fact that these stock 340's were underrated in the power, I've heard that the stock 275HP was rated at a lower RPM and the actual power was actually around 330hp. Regardless, these engines came with 10.5:1 compression from the factory according to specs, what octane were these cars running with from the factory? I can't imagine it was over 91.

What does engine pinging/knocking feel like? Just a temporary loss of power for a split second, or similar to a misfire?