If the engine cranks over at a normal speed, don't blame the battery or starter.

If the engine cranks over slow and you have HEI, check the battery voltage, or try starting while jumped to another car's battery.

Alternator has nothing to do with starting directly, but can cause low battery voltage leading to slow cranking and weak spark.

If you have a timing light, put it on a plug wire and see if it's firing while cranking.