1976 Chevy Corvette Engine will not run

My corvette died while driving down the road.
When it died, it acted as if the alternator had gone out and the car ran on the battery till it died.
When you turn the key, the engine does not turn over and the starter makes no noise. It just clicks.
The car had a complete tune-up (Plugs, wires, distributor cap and rotor button) less than 3 months ago. I replaced the alternator and the battery 2 months ago.
When the car died, I took both the alternator and the battery back thinking that was the problem.
Both were good. The alternator was outputting the correct voltage and the battery was fully charged and outputting more than the required amps.
The car has a full tank of gas. But since the engine doesn't turn over, that fact is irrelevant.
Can you tell me what is stopping the car from running?
Thanks!