Did you try running it on ether by spraying it into the intake?? That would rule out if it is a fuel problem.

 

We usually follow a procedure to determine if a starting problem is either fuel or spark related.
It seems we are jumping around all over the place and possibly guessing where the problem lies.
This wastes a lot of time and effort.
You found the cause of the no power to the dash etc , but did you completely remove the multiple connector to verify if there was any corrosion in either of the 2 components where you found the plug loose? That must be verified before going any further or you could go from place to place looking for a cause when it might have been right where you had your hands in the beginning.After you take of that , do you hear the fuel pump in the tank run for the usual 2 seconds when you first turn the key on? Yes-no ?
Then as asked if you have carb cleaner or starting fluid , did you try a short shot into the throttle body or air cleaner and see if the engine actually started even for a few seconds. Be careful , excessive stating fluid will damage the tops of pistons and should be used minimally.
It is either that or remove a spark plug to see if it is wet or dry. Again we go from what result we see there.
Can you follow this procedure and let us know what you find , maybe if necessary we can continue where to go from there.

 

Update: Replaced fuel pressure regulator. Have fuel to plugs at pressure. Both tank fuel pumps come on. got aggressive spark with MSD system. Engine still no start. Tries hard, but nothing. Replaced ECM, cap, rotor, coil, fuel filter, fuel pressure regulator already. Only thing not checked is ignition timing. Sounds just like the last time I jumped a tooth on the timing chain in my Jeep 30 years ago. At least a timing chain isn't that hard to replace.

 

Something you might check,
remove the #1 plug and unplug the plug or wires from the coil.
What we want to confirm is whether the pin broke that holds the gear on the dist shaft.
Now if you use the starter to crank the engine over you need to feel when the #1 piston comes up on the compression stroke. When you feel some pressure , stop !!! and continue turning the engine over in the same direction ( You can use the alt pulley to do this) . What you want to do is line up the timing mark TDC- Top Dead Center, on the crank pulley with the timing pointer that is mounted on the timing chain cover. You can confirm if you have the piston up at the top of it's travel by inserting like a long screwdriver into the #1 spark plug hole You will know when it is there. Now, remove the dist cap and the rotor should be pointing to the #1 spark plug tower on the cap. If it is , timing is OK, if it is not there, it might have sheared the rolled pin that holds the dist gear on the dist shaft.. If it did before removing the dist mark the dist position relative to the engine block so when you reinstall it in the same position timing will be close enough for it to start There is more to be done , but no need to blow anymore wind unless we find the pin actually sheared.