I have a case 580c that I took the injection pump off to have rebuilt, should I have brought number 1 piston up to top dead center before I took pump off which I did not. Or can I put the pump back on the way it is now? If not can I bring the number 1 piston up to top dead center on compression stroke and then install the pump? I do have a service manual but I did not read it before I started. (dumb)
Most put the machine in time before removal and check the scribe line where the pump mounts to the engine. I mostly check the scribe mark and slide it of the shaft, have it rebuilt and install new seals on the shaft and alien the dot on the end of shaft with the pump drive in the pump. Take care installing the shaft seals that they do not tare or get nicked, and are slide into the tube on the pump without damage. Those seals may allow fuel to enter the engine crankcase if damaged and will cause you to have to due them again along with a oil change or worse. If you removed the pump with the shaft in it, the key in the gear is your timing, if slide off the shaft, the dot on the shaft end and pump drive is your mark. You can get lucky and install with out looking and hit the marks right the first time or be 180 off and have to remove and realign the dots (best way) to start with. I would not turn the engine with the pump off since it holds the gear and could jump a tooth messing with it. Also fit the pump to the shaft and slide it up for the mate, remove it, then due your seal install and reinstall it, would not want to slide it on and off a lot with the new seals installed, just me.
If it's anything like an injection pump on a diesel truck, and i think it is,, it should go back on the way you took it off, like sheepfoot said, just align the scribe marks when you put it on. "If" the engine was turned with the pump off, then your in trouble.
As Sheepfoot said, if you slid the pump off it's drive shaft look in the pump and on the end of the driveshaft and line the dots up and put it on, after that you should do a timing check but it should run. There may be scribe lines on both the pump and the cover but it's not hard to check and verify the proper timing.
What brand of pump is this?