That tab mounted on the engine is your timing pointer. When you hook up a timing light properly and watch the harmonic balancer on the crankshaft, you'll see the timing marks and can determine how much advance should be set for your engine. You can adjust this by loosening your distributor holddown bolt, and carefully turning your distributor while the engine is running to adjust your timing. I've looked up timing on other websites and it seems that your 330 should be at 6 degrees (BTDC) Before Top Dead Center on cylinder number 1 at 550 RPM without the vacuum advance hooked up.