A friend bought an old York E-flat helicon from Harv (c. .65X" bore)
He asked Harv if it could be
- made into a 4-valve
- have slides that could be pushed in or pulled out from E-flat length to C length circuits
- feature on-board "storage" for the E-flat main tuning slide, so that he could change it to E-flat, if he so chose.
Harv did all of that, and pasted on some sort of King (.687") 4th valve. It appears as though Harv used a bottom valve cap as the top valve cap...Whatever...
...so my friend then asked me if I could rig up something to switch the instrument from C to E-flat on the fly, whereby he would only then need to push-in or pull out valve circuit slides, rather than having to actually swap out main slides.
...OK...so I told him "maybe" - which he took as a "YES SIR, ABSOLUTELY !!!"
I put it off (for various reasons, one of which being "How the hell am I going to manage this?" and the other being "how the hell am I going to manage this without charging more than the instrument is probably worth?")
Rummaging through parts, I grabbed a bunch of .65X" bore crap that I had (including some ancient Olds contra crap), threw it into a box, and begin the "Apollo XIII" routine.
some seemingly-conflicting requirements:
- HUNDREDS of dollars (and NOT $1XXX)
- accomplishes the objective (C to E-flat "on the fly")
- fits within the VERY restrictive allotted space
- open E-flat instrument AND open C-instrument BOTH tunable
The SEVERAL goofy ("homespun"-looking, to say the
least most) angles not only prevented a bunch of extra work (MONEY), but ALSO prevents the contraption from jabbing the player in the armpit, so...
Please don't laugh (or - actually - just go right ahead...)
The C tuning slide couldn't be allowed to "dead end" into the #1 circuit slide and (again) doing it more elegantly would have required more time/parts/MONEY, and would NOT have played ANY better.
...so one (if a SUDDEN change to E-flat is desired (as I made C "default"), one rests their left-hand fingers on the UNDERSIDES Of the valve casings, and operates this gizmo with their left THUMB.
A MAJOR MOTION PICTURE !!! 
...OR:
https://i.imgur.com/WSoK0si.mp4
) , folks' projects - bit-by-bit - are disappearing from blokeplace and migrating back to their owners, and - pretty soon (hopefully) I can get back to slicking out "attic treasures" - for your viewing-and-buying pleasure. 
