FORD 6.0 Liter Repairing The Fuel Supply System

The FICM tests at 50.5 volts so that is most likely good

was that off or running? 

if your going in to change 2 injectors that you suspect were caused by low fuel supply , change them all out and be done with it.  you can get a good set of rebuilt ones.

if you can wait there are places that rebuild your injectors for about 800 bucks, if you can't wait it is just over 1K for a set.  while your under the valve covers replace the glow plugs also, they are cheep.