Internal/external balancing

If the engine is going into a street car, not seeing 6K+ RPM's, and the rubber still looks good, I'd use it. In fact, I'm putting together a '66 engine right now for that kind of application and I'm not worried about it at all. Minor edge cracks are not big deal. You mainly don't want oil soaked rubber that's getting mushy. If it going to be raced, Fluid Dampr all the way.