Something is off here. First, and I may have missed it, but what is the exact gas you're running? What octane rating and how much ethanol is advertised?
Anyway, this shouldn't be pinging... I have more CR and piston psi than you and run on pump 93 all day long in the middle of hot North Carolina summers.
Let's do some math....
Let's assume you have a stock block with a deck height of 10.725 (big assumption), a stock stroke (3.750), and stock rod length (6.768). Those pistons have a compression height of 2.061. Granted, it's just math and not real measured numbers from the block, that means the piston is 0.021 in the hole... good.
I'm sure someone will correct me, but the 906 has a 79cc (also listed at 80 and 88. So not sure honestly...). Let's go with 79cc. Let's assume the builder threw on a very common Fel-Pro head gasket that has a compression thickness of 0.039.
Crunch the numbers and you get 10.18:1 CR, which is right at what you said from the beginning... so the numbers check out. But what doesn't check out is the pinging... that is not a high CR.
Let's go back to timing.. you mentioned using a Sniper for timing, so I'm assuming a Hyperspark for IGN box? If so, did you use the phaser tool for the distributor install and set the sniper to lock out the timing to check it? If you did... then I'm going to assume you're not dealing with a timing issue - which is what this problem sounds like if I'm honest. If the distributor isn't phased and the sniper GCF doesn't have the correct ignition reference angle set for the phase, you could be putting way over 50* of timing. I know you said 10* off the mark for setting, but just confirming you used the phase cap tool, that you locked out the timing control when you sync'ed the ignition to the sniper with a light, and the ignition reference angle is set correctly. (As a side note, sync'ing with less than 15* can cause issues, that's why Holley recommends 15*) And, importantly, that you have the right setting in the GCF for the reference angle (which if memory serves it's 57.5, but you definitely want to check that)... I'm not trying to tell you something you already know, but 90% of sniper/hyperspark issues are improper timing being set/configured.
Others already talked about hot spots... perhaps put a bore scope in the spark plug hole and look for one. If you're pining at 10.1:1 and it's a hot spot, you'll definitely see it.
Beyond what others have said... I've seen a couple super odd things cause pinging noises... like a bad wrist pin hammering the cylinder wall. A way to find that without taking the motor apart is unplug #1, drive around... plug back in and unplug #2, drive around... repeat. See if it's stops pining on a given cylinder.
I'm thinking timing... or something mechanical. OR... you're running the worst gas on the planet, which is pretty likely because of where you live.
Sidebar... Since at cruise it doesn't ping... I'm assuming you're AFR is in a good range... generally between 12.4 and 14.3? Or is it higher than 15+ when it pings?
But, they do have ethanol at the pump... if I had access to it at the pump, I'd convert to it for sure.
