Some incoherent thoughts follow:
Maybe the deck was milled at an angle by accident.
Maybe the block was line bored at some point, and ended up crooked. Not sure how someone could screw it up like this.
Also thought maybe you had mismatched pistons.
Check the bearings too and wrist pins for play.
Your compression ratio is around 10.3:1 with zero deck, not 11.1 (you must add the head gasket crushed thickness to your deck height, which is usually around .040").
That's still too high for what you are building the engine for, and that MILD CAM. If you built a hotter engine with a much bigger cam, your compression would work fine on pump gas even.
With the bigger 27cc piston dish your compression ratio would be a more reasonable 9.3:1 and that would probably be ok with high octane and a little bigger street cam. I set mine to about 9.5:1 with a bigger cam than yours, but I haven't finished the build yet. I am prepared to commit to using high octane pump gas only.
I don't build engines to run the low octane stuff. The cost difference in fuel is recovered by higher efficiency, more power extracted form the same amount of fuel because you can compress it more.
Here's a calculator for trying out different numbers:
http://johnmaherracing.com/calculators/engine-calculator/
