camlobe
It's gotta be a dodgy fuel pump.
Have you had the fuel pump bench tested and calibrated, they may have transferred the original pump from the timex engine and it is tired or whilst it has been sitting on the bench waiting to go back on the engine its gummed up. Unless the pump is doing its thing and the internal baro and fuel pressure gimcrackery is fully serviceable, you can spend a lifetime chasing it. It's the heart of those engines.
If as you you say the engine was never set up from installation, I would recommend the quickest way would be to bench test the fuel pump, fuel manifold and check the injector sizes for each pot. While you are doing that send the electrical harness to the test bench as well just to be sure. Take everything back to spec set up to the manual then it should be just fine.