Progress update:

Zero is still 100% separated and/or on leash around the Church.  I have not dropped the leash yet either.  It's coming up on the 3 week mark, it took Saffy 2 weeks -- so I don't think I should lose hope yet.  Zero does relax a lot more and look away from the cat, so that's significant but I still, obviously, do not trust him to go further.

As a result of this process I have gotten to see Church hopping across the living room in the retro 'scaredy cat' pose.  I also got to take a video of him sitting on the couch swatting at Zero's tail while he wagged it back and forth.

Zero also has some serious separation anxiety.  I was told he did better in a more open crate, so I may order one, but I have not yet (need to get more confidence in my long term income first if you catch my drift).  The big issue is if he would continue drooling at the current level in a more open crate that the carpet would be drenched.  When I say he is soaked in 20 minutes you are not taking me as literally as you should be.

I did reach out to a trainer to see what they might have to say.  The reply indicated 'bad news' that the likelihood of what I am describing being resolved is fairly low.  He is getting better about not getting into things and even had one day where I felt comfortable leaving him out while I ran for Avery without destroying anything.  He is also not immediately scratching at the door or carpet if I put him in my room to eat dinner while I ready Avery for bed, so that's progress too.  The ultimate goal is to not need to crate him, but that might be a long way off.  It is hard to get out for a walk mid-day to tire him out a bit.  If I have a meeting to call into that doesn't require me to be at my computer I am trying to walk during that window of time.