I've been playing on my community server and it looks like the humvees that spawn in the game as an event will spawn in with the hood attached (I have mine set to spawn in fully working). But if I ever need to replace the hood, there's no slot item in the menu for it.

Also, if I use Dayz++ bot in my discord to purchase one and spawn it in on the following reset. We aren't able to attach the humvee hood. There's no slot for it in the inventory and no attach options appear.