Luckily I don't want that one I am happy with my 89 dual side by side.Top core support won’t work with the 89-91 Cheyanne single headlight setup. Found that out the hard way. Like you thought they are both single headlights just different grilles and bezels. Sadly, GM changed them just enough they are not interchangeable.
When we did my 8.1 swap originally we put an ‘88 core support in to do the same setup you want to do. All was well until I tried to put the bezels on. The opening for the headlight is in a different enough location bezel won’t fit. You’ll see in my pics there’s about a years worth of time I ran it without bezels because I was looking for the right core support.
You’ll have to find an 89-91 Cheyanne core support if you want to run that grille.
As for the OP looks like he found the source for the correct one