The guards simply have a cut-out for running boards - there is no additional piece. You either use the full mudguard, or the corner trim piece. That said, using mudguards when you also have running boards kinda makes them a moot point.
I didn't look into availability, but these are the OEM part numbers for the ones to use
with running boards (as noted in post #2).
76603-60011
76604-60011
As you see in the thread below, he was in the opposite situation to you, and mistakenly received the guards that you are looking for.
forum.ih8mud.com
View attachment 3758907
I have the type he was looking for (
without running boards). It appears the guards with a cut-out end in 11, while the others (like I have) end in 21. Both are printed on mine, with the 11s including a note in Japanese. Not sure why that is.. maybe it was only a JDM option... but anyway
View attachment 3758920
My truck was totaled, and I never removed the boards, so it still has the trim pieces. It's also a 97. They may have the part number printed on them, and I could check sometime in the next day or two. Doesn't guarantee availability, although I could probably sell you mine. I'll get back to you.
Ps - if anyone wants my non-runningboard mud guards, they're for sale