GM makes a version of the plastic L31 timing cover for crate engines that wont need the CKP sensor. EGx. ZZ4, Ramjet 350 etc. That cover with the CKP sensor hole plugged is not for L31 Vortec 350 engines used in van and trucks/suvs.
CKP is used in conjection with CMP to properly fuel and time ignition for the engine.
Having or not having CKP codes will not allow or disallow the engine from running, having or not having a properly functioning CKP sensor will.