Recently would hesitate before starting, so yesterday replaced spark plugs, ignition wires, distributor cap and rotor head (new battery in October).
After all that, now it plain won't start. Engine is turning, lights, horn, radio, all work....ignition just won't catch.
Could it be the ignition coil or igniter unit (both inside the distributor housing)?
Any suggestions?

First, when you turn the key on, do you see the check engine light come on for 2 seconds and go off?
If so, do you hear the fuel pump run when this happens?

Were the old spark plugs soaked with fuel?

You'll need to check for spark, pull a plug wire, put a screwdriver in the end of the wire and put part of the screwdriver about a half inch away from a good clean metal part of the engine. Crank it over, is there spark jumping from the screwdriver to ground?

If not, you could have a bad coil, bad igniter or bad distributor.

Start with what I've asked and we can go from there.

How many miles are on your car? What ignition parts did you install?