These are pretty popular and well made Combine models: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=262326562 and maybe they can be in Background NPCs, with the Ghillie as some kind of sniper and the pilot as some kind of soldier that gets sent along with tanks. This is just an idea though, so it might not actually be possible.

Obviously they would be included as optional compatible models in the description, because Background NPCs has not included a single custom model or sound and it'd be nice to keep it like that.