Rebuilt Slant 6 but No Spark help!

Let's start with "year make and model," then add "what is it exactly" you are using for an ignition system?

Breaker points?
Pertronics?
HEI conversion?
Mopar ECU?
Other?

"What have you checked?"

Voltage to coil? Voltage to coil DURING CRANKING?

Breaker points? Are they actually opening and closing? Put a meter on the coil NEG...where the wire to the dist connects. Rotating the engine at some point you should see battery voltage, more rotation should result in very low voltage at coil NEG

You MUST have a good condenser (capacitor) in the distributor