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.
