The vehichle is a '73 Dodge W200 truck, I started it up yesterday, and let it run for a while, it started popping and backfiring real bad until it stalled out. Now it has no spark at all. I have replaced the ballast, ECU, and the coil and still nothing. I have power to both sides of the coil with the key on and no spark coming out of it.

take off the wire(s)on the coil neg pri terminal and w a jumper wire w alligator clips on each end ground the coil male terminal (not the wire you removed from the terminal) to ground repeatedly like Morse Code and see if that makes the large coil secondary wire (dist end) helpd 1/4" from ground make sparks (key on). If so prob is in the dist (pickup/gap etc) unless you have a loose connection somewhere such as the bulkhead (seperate it & clean/check the brass terminals) or ign sw contacts etc but start by opening the dist & see what you see

Just checked the gap on pick up in the dist. and its fine.

Ohm it & see what the Morse Code test does

Have you checked that the distributor is turning while the engine is cranking? The timing chain may have slipped or come off. That happened to me one time.