Could one of the pulleys be out by 360'
ie the pump injecting on the exhaust stroke
Don't think that can happen Andyg, provided the cam and pump are timed together the crank doesn't care which tdc it's on.
Assuming you've checked to determine that the pump is actually injecting, does the exhaust smoke while cranking? did you bleed injector pipes?, it may be possible that the distributor timing (internal) of the pump is out, you don't say what pump you have but I managed to do it with the EPIC, I dismantled mine to fix leaks, and without any information available didn't know what was in there till it all fell out, managed to reassemble it with distributor a quarter turn out,
now it's running perfectly but the timing points don't line up.
Do you know if yours was right before the trouble with the belt?.