[turf3]

I'd add the extension.

I have done a lot of this work by soft soldering; the very important key is to have as near to zero gap as possible. With minimal gap, the strength of the solder is not a key factor in the durabiltiy of the joint. If you can't do the fine fitting to achieve that, then the strength of the solder becomes a factor and you'll have to silver solder/braze it.

 

[turf3]

Well, if you were to lengthen that C# rod by some heavy swaging in the middle of its length, you wouldn't have to fool with either post; you'd reduce the misalignment at the north end; and the horn could always be returned to original configuration very easily.

I'd suggest that the misalignment of the keys won't be noticed in actual play, but if it is, one could solder a 4 -5 mm extension onto the end of the C# to make it even. (You have to leave a hole for the roller's screw.) We're not talking about high collector value horns here; just modify as needed.

I assume the swapped key lines up OK down at the C# pad area? Spring mounts line up? G# linkage OK?

 

[turf3]

Turf3, this is not a hollow tube, it is a long solid rod, not sure you could swage this.

I have done that very thing, to lengthen a rod (brass). Though I didn't do it with swaging pliers. I just gently peened the rod against the anvil of a vise, working my way round and round the rod, till it reached the desired length. Easy peasy.

 

[turf3]

I'd hammer swage that rod a little longer (so it stays the way you've pushed it up for the picture) and declare victory. That table looks as well aligned as several of my horns that still have all their original parts.

 

[turf3]

All right, you've got some choices.

1) Lengthen the rod by swaging - rejected after experimentation as described above.
2) Lengthen the rod by cutting in two and inserting a sleeve - will absolutely work, but it will be pretty visible too.
3) Move the lower post (don't need to unsolder, just bend it over a bit)
4) Ream the pivot screw seat on the lower post (might not be enough meat there).

Whatever you do, you'll want to adjust the pivot screw joints for minimal play and no binding.

 

[turf3]

OP finished the project back in February and has been playing the completed horn for 10 months now.