Specs, nothing official. But saw somewhere that likely recommended in general is a reasonably good i7. One of those mid to higher end nVidia cards that support real time raytracing, or comparable AMD. Graphically it obviously looks pretty demanding.
And yes for mega-million dollar AAA titles modtools are long gone except for, maybe, specific and limited things. Zombies in BO3 for example. Checked out the BO3 tools and they are a lot more complicated in every way. In this case they are trying, again, multi-platform so any mod would exclude anyone on a console. And they dont want to do that.
Most cod4/5 modders have moved on to other game development like UE4 anyways. Those that do still do it, its because they enjoy making things and the challenge. Despite the headaches it causes all around.