Have you verified this with a timing light on each of the wires?

A jumped timing chain, a bad rotor (or cap/rotor if rotor strikes the cap), points/dwell, bad coil, loose coil wires, or broken/missing distributor gear drive pin are common suspects.

Check for consistent power to the coil with a test lamp on coil +. It should light and hold steady while cranking. If not, check for a loose ignition wire to coil +.

Test for point operation with either timing light on the coil to distributor spark wire or with a test lamp from coil - to ground. Either way you should get a rapidly, evenly flashing light. If not, check to see if your distributor is bolted down tight, or it may have lost its initial timing. Check cap and rotor, points, coil to distributor primary wire, distributor drive gear pin (if this is bad, rotor will turn by hand with the distributor installed). Also check the advance springs and weights, make sure none are broken or stuck.