I had an '87 for a parts vehicle and was going to swap the grill into my '88.5 (just opposite of what you are planning). I had both grills - they are different and will not interchange. Have since sold the parts vehicle, but I'm sure if you look around, you could find an '87 grill. Good luck.
The 88.5 grille will fit into the opening ok, but the bolt holes in the corners will not line up with the mounting tabs. It can be made to fit with some fabrication, but is not a direct bolt on interchange.
CrowHorse: Thank you for your offer, I think I'm just gonna stick with my '88 grille. If something happens to this one, I may consider trying to swap an '88 1/2 grille to replace it. But its no high priority for me right now.