They made 7 1/4's with sure grips also. Not very common though. You can tell if you have one by jacking the rear of the car up (wheels blocked please), putting the car in neutral and with the brake off, rotate one of the rear wheels. If both rear wheel turn the same direction, you have a sure grip. If they turn opposite directions or only one turns with the driveshaft, you don't have a sure grip. (or it's completely worn out) I think there are some upgraded side gears and spider gears available for the 7 1/4. Those are the weakest part of the rear so if you upgrade them, you should be able to drive normally without worry. If you're going to jump on it, all bets are off.
