Probably the damper (Lower pulley) has slipped to show the timing mark
so far out. The timing might be OK but you can't use the timing light.
Maybe you need to confirm cam to crank timing without the light.

Was the engine OK then suddenly ran bad.

You need to some general trouble shooting.
Check for a plugged air filter and for vacuum leaks.
look at each plug for clues. Just because you just replace a distributor cap and wires, doesn't insure that they are working. suspect everything.

No one has come up with a test for sticking your hand over the exhaust pipe to check for an exhaust/cat restriction. See if the exhaust seems normal at the exhaust pipe.

Bill