Oh how I missed you my friend... Glad to have you back...
Let me take a crack at answering this, and then maybe jbtsax will chime in as well. I'm curious as to what his experience with this is.
I have a couple of near minty Tonekings like those of which you speak. Both my alto and tenor came with plastic angelwings when I bought them. The tenor had had a
custom angel wing made, while the alto had the
original Lucite angel wing with the tail end broken off.
When I had each restored, I managed to track down two original JK metal replacement angel wings and clothes guards from Gerhard Keilwerth's shop shortly after his passing. (These are unfortunately no longer available through his former shop apparently.) Now both horns are just decked out in original JK bits (
tenor,
alto).
Both of these horns are incredibly free-blowing. They have a huge tone. (The tenor even more so than the alto.) Their volume is massive, and can easily drown out contemporary horns in a section. When I play them, I am always cognizant that I have to adjust my playing--compared many of my other horns like my Mark VIs, Hohners, Conns, or even my Zeph tenor--when I'm rehearsing with the big band I play in. It's not uncommon for my volume to be too loud when playing these horns.
In short, I don't find that the key guard on the JK's interfere with the tone in the slightest. Of course the only way to know for sure would be to record the same piece both with and sans key guard.
If you really want an answer if key guards make a difference in tone, look no further than the eyebrow key guards in my
Hohners, or on older Zephs, on the Weros, and a few other select saxophones.
To answer this question, I will say the same thing I mentioned re: the removal of lacquer and the correlation to greater vibration and possible tonal change.
I believe that before the design and manufacturing of saxophones was computerized like it is today, horns tended to be far more individual. For me, it makes sense that the sound of a saxophone, comes to a degree from the shape of its bore.
This is why, in part, D&J had such success with their tenors. The D&J tenors sounded just like the JK Tonekings & The New Kings. Different models/makes had different bore designs. We know that the bore plays an important part in the tone, which is why the newer Mark VI for example, sound "brighter" than the older ones: Selmer changed the bore over the course of the Mark VI's production run.
Add hand-craftsmanship into the mix, and you have the possibility to an endless set of variables that all can possibly have an affect on the tone.
Furthermore, we know that the closer to the source of the tone (the lungs, pharynx, mouth, etc) you make changes, the greater the effect on the tone. That's why changes to the MP, reed, and possibly the neck, will net a player much better results than changing his/her horn.
Changing key guards is as about as far away from the source of tone as you can get, and which is why I am not sure key guards have any bearing in a horn's tone one way or the other.