Need input from the brain trust; fuel or ignition redux

I just started my 1971 Duster w/stock 318 for the first time in many years (like more than a decade). I replaced the gas tank, fuel line, coil, distributor cap and rotor, and then changed the oil and ran it on several occasions for a total of about 100 miles. I fired it up again last week and got about a mile down the road when I felt the engine chug. I turned the vehicle around and went back in the direction of home and the engine backfired a few times and then died completely, leaving me to push the car back into the garage. It had totally lost spark, as far as I can tell. I then replaced the coil, cap and rotor, ECM, and ballast with new, and the car fired and seemed to idle ok; but then it would seem to lose power and quickly die again when I pressed the accelerator. I've got a brand new electric ignition and 4-bbl carb ready to install but I need help from some Mopar guys down the street, and I'd like to take it to them in working condition so they don't have to waste a bunch of time trouble shooting. I don't quite have the technical skills to upgrade the ignition (it's a Jegs kit that requires some extra wiring for the ECM). Is there something else I'm missing, or does anyone know off-hand what the problem is? Is this actually a carb/fuel problem?