Just went through this scenerio myself. Remove the injector pump timing plate, and have an observer make sure the shaft is turning when you crank the engine over. Assuming the pump shaft turns with the engine, remove the fuel shut off cover on the side of the pump below the hydraulic head, and cut the safety wire on the fuel control shaft retaining clamp. Remove the clamp
and then unhook the governor rod from the fuel control by carefully removing the small clip. Pull the fuel control shaft out and
make sure you retrieve the small key/pin from the fuel control plate if it didn't come out with the fuel control shaft. You may find a small mirror helpful to do this and the next step. If the pin is in one piece, then carefully using a small screwdriver, verify the
fuel control block moves up and down on the hydraulic head mainshaft freely. At this point you either found something wrong
or you need to remove the hydraulic head to look deeper for the trouble. I used a white automotive paint touch-up tube with a small brush to mark the gear tooth (or groove if in between teeth) that is in line with the fixed pointer just above the gear. This is for reference for when you reassemble, so you don't have to roll the engine over to line up all the timing marks.
Remove injector lines from the top of the hydraulic head and the fuel lines from the front and rear off the head as well. Remove the 4 retaining nuts and clamping spacers and the head will pull straight out. You may find the thrust button and retaining clip laying in the
cavity that the head was just removed from. It is possible that the hydraulic head piston is/was sticky and allowed the thrust button and clip to fall off. This would prevent you from getting sufficient stroke to pump fuel through the injector lines. I however, was not that lucky, the fuel control block seized to the piston shaft, sticking the piston near the full up position, breaking the fuel control key/pin and dropping the thrust button and clip off too. Cure for me was a new hydraulic head, but you may be fortunate enough to just be able to clean everything up, and reassemble in reverse order. Good luck!