I agree with "ponymare". If it starts while cranking and then dies the second you release the ignition switch it could be a burned-out ballast resistor, if it has one. If it was wired like most factory 12V vehicles were like mustangs, in the crank position the coil is given a full 12 volts from the starter solenoid. This produces a hotter spark for easier starting. When the key is released back to the run position the voltage then goes through the ballast resister. If the resister burns out the coil will not get any voltage in the run position. We had a lot of Dodge vans in the phone company fleet that took that same external ceramic resistor a lot of hot rodders use them. It was fairly common for them to fail. They ran while you were cranking the engine and quit when you returned the switch to the run position. One of the fastest fixes and repairs you can diagnose. If you have the external resister bypass it an see if it will run. Don't leave it bypassed for too long or it will burnout the coil.
If it's a fuel problem, you can spray starting fluid, carb cleaner or brake clean into the carb to keep it running after it starts. If it runs on the spray cans you know it's a fuel problem. If not, it's an ignition problem. Does that Holley have a site plug for the float bowl level.
If it was fuel it would not instantly turn off after it starts, unless it was only running on the squirt from the accelerator pump and then not getting any more fuel There is a difference between how an engine quits if it runs out of fuel or runs out of spark. Just that a couple seconds of sound usually send me in one of those directions. Its 45 years of hearing the differences and sometimes still jump to conclusions and am wrong. What's important is when this fixed you will be a better mechanic. I admire people that work on their own cars. If you can fix cars, you can fix most things. The most important thing is to understand how each system works. The fuel system, the ignition system, how basic electricity works... That is the key to fixing this stuff. None of it is hard if you're interested in it.
Don't overlook coincidences. You can put a new carb on and have the resister burnout at the same time. The "universe" loves to mess with mechanics. I have had some really weird coincidences happen during my career that made me glad I was working on fleet vehicles and not on customers vehicles. W' called it drive them in a push them out at work. we were thinking, all I did was change the oil and now the trans won't move. Really, you wait until I sit in the seat to break!
I was thinking about this some more. It could possibly the ignition switch could be bad; I only saw it happen a few times in my career. Just like the resistor, the clue would be that it instantly shuts off when it returns to the run position. You can jump 12 volts directly to the positive side of the coil for just a minute or two and bypass the entire switch, resistor and wiring and then crank it. If it starts you won't be able to turn it off without removing that wire. I have a arsenal of different gauge and length wires with alligator clips for bypassing stuff. It' not a bad ideas to carry one in your emergency tool kit.
