Check your fuel pump I put a new one on my 73 340 duster and it would run a few miles then quit,took it off and installed my Old pump and it runs great.
I like PPG base coat clear coat,The clear is just one more step and will last for years,Use a good epoxy primmer and then primer surfacer and you will have no problems,Painted the last three cars this way and they looked great.
HI last April i managed to get my hands on a 1973 340 SPACE DUSTER, My best friend growing up bought the car in 1974,I rode to high school in this car,It was in his barn since 1999,It was Black with Black interior,bucket seats automatic on the floor getting ready for new paint now.