Hey fellas I was wondering if anyone knew what the 5/8" threaded hole on edelbrock or most SBC aluminum heads are for. The hole is on each head on the left hand side, right below where you mount you exhaust headers or manifolds. I just plugged mine with a pipe plug. Anybody know? I have attached a pic. The hole I'm talking about is the one that the arrows are NOT pointing to. to the left of the arrows.