One thing, not directly answering your question - Boosh split-bellkey baritones had a tendency to be unstable around low E and low D (warble/gurgle).
I have never heard this before.
I own a TT bari and it does not do this with my JJ DV NY, a Link STM, a Link Tone Edge, or a Rousseau Classic, all of which play fairly well in tune on the horn. (Yeah the Rousseau shocked me too!) I don't remember it doing that with a pickle barrel either.
It does warble with a couple of mouthpieces I've tried, but those pieces were comically out of tune anyway so I can't say I'm surprised other issues appeared as well.
The TT bari's right hand ergonomics don't get along with short fingers. Modifying the RH side keys to sit a bit lower wouldn't be too expensive if it is a problem. My fingers are long so I've never had an issue with it at all - consequently I need a huge riser on LH palm D, but that's cheap and easy.
I'm sure an Aristocrat would be a bit better, but I've never tried one. I would definitely appreciate the extra inline low Bb touch, and the thought has crossed my mind to simply have an extension made and brazed onto my TT.
I tried a very early transitional Zephyr, but the bore was still the '20s Voll True. I had no issues with the ergos, so I wouldn't expect any with a later King. Pretty similar to the TT, except the RH and LH palm keys both sat lower. It was more mouthpiece-picky than my Buescher though, but again, not really a Zephyr.
FWIW I can't stand the RH ergos of a Conn bari. My right fingers and wrist end up at an uncomfortable angle to get my fingertips on the pearls and pinky table correctly, mostly just because the horn sits so damn low and my fingers are long. Which is fine, I prefer the way a Buescher plays anyway!