OHHHH, you are talking about the engine, i was thinking about the actual machine, sorry.
I have done this before now. You don't need to remove the plate, you can actually do it with it still in place. Remove the 2 nuts on the arm and slide the arm off, remove the key then remove the plastic or metal (they are different) block that looks like a thick washer. Under here you will have an O ring, simply replace this and re-assemble, you are then set. If its tight, you can remove the plate, the springs should not fall out. Use long nose pliers and un-do them together. The way they are attached to the governor arm at the injector pump makes it quite hard for them to simply fall out. If you are worried, attach a small piece if wire to them so you can get them easily when you need to put the plate back in.
Now, the arm may be a little stiff, you can lever it off with screwdrivers but be careful of the block under it, i have had one that was very brittle, i replaced it with an aluminum one.
If you need more info, just yell.