Well... any live axle Jeep that's 40 years old could have some stress crack issues. The usual place for cracks is in the vicinity of the big front cross member, especially near the steering bracket. Anywhere you have flexible into rigid, fatigue cracks are more likely. I would also look around the spring hangers, esp. the rear hangers of teh front springs. That seems to be a stress point on many models of Jeeps. However, I think that breakage is more associated with abuse (big air, ie Rat Patrol action) than age. If it checks out ok, you should be fine if you don't try to launch it.