ok matt have you disconnected the fuel injector supply pipes at the metering head or the injector itself to check for flow, or do you have them all connected and injectors out of there seats. the only thing left i can think of and something you havent changed is the injectors themselves,all be it highly unlikely the 4 of them are blocked solid,the only thing that can stop fuel getting to the injectors in the metering head is the fuel plunger inside the unit and connected to the sensor plate so the problem is there somewhere.dont know if you can but you could try connecting an injector supply to the cold start supply to see if fuel pressure is squirting out the end of each of the injectors
keep me posted and we.ll solve it somehow