Just went through this myself. Look at the front bunch of pages of the parts TM, find out what your code is for your truck, then find the proper parts number in the schematic. I actually ended up buying the wrong two parts, epay had a listing for superseding all others(it didn't, It wasn't for my M1038 and neither of the two parts fit. There were two numbers for the parts in the TM, I had picked the bottom two, Thought they were just substitutes. They weren't, they are for heavier duty vehicles.
H13 is your UOC code for M998 Page 33 of the 1rst parts TM PAOZZ 2530012491577 98349 L-20-MA-133-A-11 IDLER ARM,STEERING,................. 1
UOC:AVY,A11,A13,A14,A15,A20,A24,A25,
A26,A27,B16,B17,B18,HVY,H11,H13,H14,
H15,H16,H17,H18,H20,H21,H24,H25,H26,
H27,H28,MMM
7 PAOZZ 2530012528362 98349 L-20-MA-132-A-11 ARM,STEERING GEAR................... 1
UOC:AVY,A11,A13,A14,A15,A20,A24,A25,
A26,A27,B16,B17,B18,HVY,H11,H13,H14,
H15,H16,H17,H18,H20,H21,H24,H25,H26,
H27,H28,MMM
You have the right two numbers in your first post.