I have some other things to do and will come back and read everything BUT your logic on the fuel may be logical but dead wrong
The computer adjusts the fuel based on inputs, you don't adjust using using base pressure different than what you tell the computer. If that was required there would be no need for injector tuning, nor would there be all the sensors to help. The ONLY job of the computer is injector timing, pulse, and duration (and fast idle) everything else is an input. When you try to trick the computer, it has a false base to make decisions. Not to mention, as you drop pressure, the pattern gets messier and messier, eventually dribbling at low duty cycles
1 - The computer accounts for 2 sets of injectors when you select dual throttle bodies and adjusts, your 1/2 logic is already accounted for when you chose dual TBs
2 - The computer uses injector pulse width and injector slope to determine how much fuel is entered into the engine at the input pressure. So if you adjust the pressure differently than the input, it no longer accurately adjusts
3 - You may think your TDC is close, and it likely is, but your method will NOT get it exact, close but not exact. I am not blaming anything on timing, but realize you could easily be a few degrees off.
4 - Take all the plugs out, go either way, the crank bolt won't loosen, if it does, you have something else wrong or the bolt is too loose.
5 - Too much injector is almost impossible, its not a carb, the computer just sprays for a shorter duration or a different shaped flow curve.
6 - I really don't like what the EFI tech is telling you.
Those plugs are indicative of a bad tune, I'd put a set of cheap Autolites in it, then go back and rebuild the initial tune carefully. You can play with those after it's dialed in, but they won't help you, just a shiny object
If you get me the data I asked for I will help the best I can, but without seeing what the computer is telling you, there is no way to tune other than just starting over and being careful to make sure you don't fat finger the data