slant six cranks but won't start

Sometimes I use a little Thrust (the can at pretty much any auto parts store) to spray into the carb. Maybe the engine is flooded? If you can smell a strong gas odor under the hood, then its most likely flooded.

For flooded engines, I take a screwdriver and hold the choke open to let the gas evaporate faster. Let it sit for a little and then try.

Definitely go over the basics like what 67Dart273 said, you don't want to crank and crank until the battery is dead.

Also... on the points suggestion, maybe try a Pertronix electronic conversion? It takes away the need for the points ignition system completely.

Good luck.