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Sorry about that. I'm not so good at typing out exactly what I mean.

This isn't a question about adding the valve, but rather changing the porting (or knuckles) to king style to allow you to orient the valve section however you please.

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So here is the first knuckle of a 20k valveset. The knuckle comes out of the casing curved. It seems no matter where you cut it there's not going to be a nice spot to fit a ferrule. A King style valveset would be super nice, but I'm wondering how you would fit the connecting ferrule to a curved knuckle?

I hope this is a better asked question...

The only "art" of this is to move the metal around to where you need it. In your case, the knuckle "stumps" have to be reshaped. I had to do that, too.

I cut them off very close to the casing wall and bent them into the shape I wanted, using some small pliers that have jaws that are well suited to this sort of work.

I then dropped in the worst of the two remaining pistons so that the port being worked on was backed by a solid wall, which helps to prevent the knuckle from pushing into the casing while being bent into shape.

After that, I fit mini-ferrules onto the knuckle stumps and expanded them to fit the ferrule perfectly using a flute headjoint expander, which works great to open up, re-round, and smooth valve knuckles. (The piston "backer" was rotated and moved up or down and then taped in place as needed to back each port in turn.)

Once each ferrule was fitted to its knuckle stump it was ready to be soldered into place. However, I have to undo this, as I want to do a more accurate job of leveling each knuckle end, and I need to cut new mini-ferrules using my mini miter saw so that they are actually straight. (I eyeballed the ones in the photos, and some of them are pretty crooked.) I also want to make the mini-ferrules deeper. I want each one to have an insertion depth of .25" to make the soft solder joint to the slide tube stronger. (The end on the knuckle can be very short because the joint will be silver soldered, and, therefore, very strong.)

I hope I did a better job answering your question now. Thanks for the follow-up explanation. I understood what you were asking much more fully that time.

I like the solution for eliminating the sousaphone-tilt knuckles by cutting them off and converting the exit ports to “King style“.

It also allows me the option of using them as a vertical set, which makes setting them more deeply into the bugle an easier task.

The clock is running, and I need to get really serious about getting things in the attic all put in the condition which will coax consumers into smiling really large smiles, and getting all that stuff sold.
I couldn’t resist this recent Holton project, because it was just so damned promising, and (thankfully) it kept its promises to me - as far as what it offers me...
...but I just need to be disciplining myself to keep most of the rest of the projects in their cardboard boxes for now, and get those desirable-to-others instruments fixed up and sold.
(Parenthetically, the stuff I plan to do to that model 90 Miraphone Kaiser - and even run-of-the-mill complete restoration jobs - really do not qualify as “projects“, because they do not involve hundreds and hundreds of hours of time.)
That having been said, if/when I undertake another project, I will probably find myself stealing your “King-style” flexible knuckle technique, there. Even with valvesets that are nearly completely already set up for the desired goals, one or two of the knuckles could be cut off in that manner to achieve just what is desired - and without compromise.
I have opened up casing ports - before - to the OD of replacement knuckles and silver braised them in place, but those operations were followed up by a complete piston/casing rebuilding, so the damage caused by the extreme heat wasn’t that much of an issue. Your technique can circumvent the (now: quadrupled) expense of rebuilding, if it is not necessary in the first place.
It obviously offers endless possibilities, as far as working around problems and obstacles.

I have fully recovered from my surgery, so I need to get on the stick and prep some horns for sale (or to be returned to their owner). Then I have a few trips to make in the car, which is not ready for the road, so I have *that* to deal with, too.

Ugh…

This King-ish way to work with knuckles is what allowed me to adjust the Holton's 3rd valve lower knuckle to match the span of the wider Miraphone crook. Being able to make that crook fit made me quite happy, I will admit.

The knuckle is a little misshapen due to having been expanded on the end to mate up with the .5mm larger tubing. It was also misshapen a bit when I bought the horn from Mark.