Welcome to JUST ANSWER heavy equipment. With years of experience, I look forward to doing my best to help.
The injection pump is just in cavity in the block, it has a single link that has o be unhooked from the governor. See second picture, # 3 gasket and cover, remove it and unpin the link. Then the nuts can be removed and the injection pump lifted out.
# 5 is the shims used to set the timing. Keep them together when removing the pump and put the same amount back. You add or remove shims to change timing if required.
Let me know. Thank you.