I'm probably not going to be here much for the next couple days. My grandfather went into the hospital and was diagnosed with a hematoma (sp?) in the brain. It's nothing they can correct and he was on blood thinners so it's just a matter of time.
Would you please set your crank to 0?BTDC, take the cover off of the CPS and post a picture of the internals? I'd like to see if it's clocked correctly internally.
The 660's would make for rough running and starting but it should still burn and not fire back into the intake plenum. I'm not saying it's not possible but I don't think it's very likely. Have you inspected the ISCV and the check valve to make sure enough air is entering the manifold when the throttle is closed?