How do you adjust the tension on a 1978 Datsun 620 bulletside?

To adjust the tension on a 1978 Datsun 620 bulletside, locate the alternator or belt tensioner. Loosen the mounting bolts slightly, then adjust the tension by moving the alternator or tensioner to achieve the desired belt tightness—there should be about half an inch of play. Once the tension is correct, tighten the bolts securely to maintain the adjustment. Always check the belt for wear or damage during this process.