Might be the timing way to far advanced. Even with a vacuum leak it Should run....if anything it will start and runaway pending on where the leak is. Guys have been able to get their engines to run....and they wouldn't want to rev up....Timing was to retarded.....other times it spins over and over and over....hit some starting fluid...pops..sputters and dies....Timing to far advanced or your 180 degrees off. Firing order is 1-5-3-6-2-4 so start with number 1 on your distributor and see where it is. Factory would have it at the terminal Right next to cylinder 1. If they're off one terminal your 180 off and you'll never get it right by turning the cap back and forth. Verify you have fuel going To the carb by spinning the engine over and watching the fuel pump gas into a bottle....then spin the engine over while looking down the throat of the carb(don't let it back fire on your eyebrows. lol) and see if fuel is squirting from the jets...if it is...the fuel is Not the major issue. Then move to spark...if you have a weak spark it won't want to start on gas. Your coil may not be getting proper voltage....Also check the points gap and make sure they're not to wide or to close. .018 is a general setting. Verify you have good spark....then crank on it while someone is moving the dizzy back and forth until it starts....get it to where it will run....let it get hot and set your initial timing to 8-10 for the time being. You'll know if you have vacuum leaks, especially when it gets hot. That's how I do my engines...so far so good! lol
