351m, hei distributor , Holley 670 truck avenger.

Manually reset timing, rebuilt carb, fixed vacuum leaks.

Cranks, but doesn't run. getting fuel and air.

What's the best way to test if it's getting spark?

 

Pull the coil wire out of the distributor, hold the end of the coil wire about 1/4" away from a good ground (engine block) and crank the engine over.
You should see a strong blue/white spark that is consistent, not hit or miss.

 

I'm not familiar with HEI distributors at all, any recommendations on where to research hei troubleshooting? I'll try and find some hei conversion threads tomorrow to make sure it's installed correctly

 

Just like Mike mentioned, if your sure you are getting fuel, you need to check for a good blue spark at the plug.
If you have a second person to turn the ignition key for you. You could remove any spark plug, plug the spark plug wire to the spark plug, and lay it on the engine someplace that has some clean bear metal. Then have someone turn the key as you watch for that plug to spark. Works better it it isn't real bright out.
If your sure you not, getting a spark. Remove the distributor cap, and again have someone turn the key, and watch to see if the shaft from the distributor is turning. If it isn't I'd remove the distributor, and check to see if the gear isn't damaged. If it's good, then it may be time for a timing chain and gears.

Unk Bob

 

Oh Man! I didn't catch the HEI part of the original post. No coil wire to pull out, sorry.
Pull a plug wire off and stick a phillips screwdriver in the end. Hold the screwdriver close to a good ground and crank. You should see the spark. Only difference, instead of four sparks per revolution, now you'll only see 1 spark every other revolution.