We had a timing belt fail on our 86 745T while it was traveling on the interstate at 3000 rpm, 76 mph. All I had to do was replace the broken belt, and eventually the front seal which had been damaged by belt parts. I don't know what the clearances are, but manufacturing tolerances can accumulate to where non-interference engines become interference engines like on the VW Quantum we used to own. That non-interference engine bent two exhaust valves when the timing belt tensioner seized and smoked the belt. About twenty percent of those non-interference engines interfere. The tried and true method of modeling clay on top of the pistons at TDC while rotating the cam will reveal the actual valve to piston clearance with broken timing belt.