Firing order should be 1-5-3-6-2-4. Look for it on the intake manifold at cylinder #1, it may be cast on top of it like it is on my straight 6 cyl chevy.
Pop the distributor cap off, turn the engine over with the starter and make sure the distributor rotor actually turns.
Use a new plug at the end of a plug wire and press it against the engine, then have someone crank the engine over and watch for spark.
Double check that your timing is set at #1 TDC: align the timing marks, remove valve cover and make sure both #1 valves are closed. If one is open, you are at the wrong stroke... turn the crank one full turn and recheck that the valves are both closed, and timing marks are aligned. Then see where your distributor rotor points at and put the #1 wire there, and the rest according to teh firing order.
I don't know what you have in regards XXXXX XXXXX HEI ignition... does that mean it was retrofitted and teh engine used to have conventional points&condensor distributor in it? Do you still have them so you could try to see if they would make it run?
Does your coil wire run through a ballast resistor? The HEI stuff most likely doesn't like it if you are still using the same power wire. I can't really help you much with the non-stock ignition, I think this engine never came with HEI... but I am not sure. Mine doesn't have one, it's all stone age stuff on mine. I had similar problems and it was the points and condenser. Turns out someone had replaced the coil with one that required an external ballast resistor, and the car did not have one. Points and condensor would go bad in just one day, sometimes a couple of days. Too much power from the coil.