I was asked to add a second valve in G to this King 3B Silversonic trombone. I used a valve from a donor 3B and cut the tubing down from F to G. It was necessary to put the 2nd valve first in line before the 1st valve in order to make things fit, but changing where the linkages go enabled the F valve to be operated by the thumb and the G valve to be operated by the finger, as they would be on a normal bass trombone. It was a bit of an engineering puzzle, but I was able to fit it all together by angling the valve wraps away from each other, and fabricating a short neckpipe piece to transition from the valves to the tuning slide. Here is the finished product: