This series of engines is one of my favorites, simple, rugged, and easy to work on/troubleshoot. The screw terminal powerpacks make troubleshooting much simpler.
Just want to make sure I have all the facts. You were cranking with the plugs out, the battery is fully charged, and cranking speed is not an issue. You swapped a known good powerpack from another engine which changed nothing. I am assuming the engine probably won’t start or run because it is on only two cylinders. Tell us just how you are checking for spark. I am assuming you are just grounding plugs and cranking the engine with the plugs out. This engine should be able to jump a 7/16" gap on a conventional spark tester. I understand you are doing what you can to test spark, but please know that cranking the engine with the plugs out is a real fire hazard, might not be great for the coils as well.
Like Roj says, please start with the simple stuff and make no assumptions. So, the simplest test is to remove the black/yellow stop lead from the powerpack and restest. I realize that it is unlikely a partially shorted stop circuit could affect spark this way, but anything is possible with electronics and this elimination test is simple and easy to do.
Next, it is important to realize that that aluminum support bracket that holds all the ignition components is not grounded directly to the block, there are a few ground straps that supply the ground, check bracket ground with an ohmmeter set on the low scale, check and clean the ground straps.
The next step is where the nice screw terminal powerpack comes in handy. Not likely you have two bad coils, but anything IS possible. So, how about swapping #2 & #4 coil leads on the powerpack with #1 and #3 coil leads, then check for spark again. If #1 and #3 coils now spark, it is safe to assume the coils are OK for now, there is no powerpack output to the #1 and #3 pack terminals for some reason. Do you understand my methodology here?
Please don’t forget to reinstall the coil leads on the proper pack terminals, there should be a decal on the pack cover showing were all the terminals belong. Next, I would swap the sensor leads on the powerpack. There are only two sensors, one for #1 and #3, the other for #2 and #4. So, the next test would be swapping the two sensors. Simply connect the #1 & #3 sensors to the #2 #4 outlets on the powerpack and vica versa. I’m suspecting you will find the problem during this test. So, with the sensors swapped on the pack, if the #1 and #3 coils now fire, then the problem is with the sensors. If the #1&#3 coils still don’t fire with the sensors swapped, we have missed something or made a wrong "assumption".
These tests can be a little confusing, so it is easy to head off in the wrong direction based on confusion or wrong assumption, so take your time and be sure to reconnect all the leads properly to the pack after each test, before beginning the next one.
Once we isolate the problem, and I think it will be with the sensors, we need to go back and check every ignition component with an ohm meter and do the output tests…
Hope this helps, I know that ONE picture would be worth much more than several hundred of my words. Let me know if and where you are confused if my instructions don’t make sense to you….