If your vehicle is equipped with a V8 engine, remove the air cleaner assembly and cover the carburetor opening with a clean rag. Position the number one piston at top dead center (TDC) on the compression stroke by detaching each spark plug wire and removing all spark plugs from the engine. Locate the number one cylinder spark plug wire, trace it back to the distributor, mark the distributor body below the terminal for the number one spark plug wire, then remove the cap and wires from the distributor. Use a wrench or socket on the large bolt at the front of the crankshaft and turn it clockwise until the groove in the crankshaft pulley aligns with the O (zero) on the timing mark tag, ensuring the rotor points at the mark on the distributor body; if not, turn the crankshaft one more complete revolution. Disconnect the hose from the distributor vacuum advance unit if applicable and unplug the distributor wiring harness connector(s). Scribe a line on the distributor body and make a corresponding mark on the engine block, then remove the hold-down bolt and clamp to carefully lift out the distributor, using an oil filter wrench if it is stuck. Do not crank the engine until the distributor is reinstalled, ensuring the O-ring on the lower part of the distributor body is in good condition. To install the distributor, align the mating marks and slide it into place, possibly moving the shaft back-and-forth to engage the gear, ensuring the rotor points at the mark on the distributor. Install the clamp and bolt finger tight, replace the spark plugs, and install the plug wires. Finally, install the distributor cap and connect the wires and vacuum hose, then check the ignition timing.