I have figured out the possible answer to one of my questions. See http://www.zoindustrial.com/products/brass-series/Tuba/526.html My horn from Schiller may be the ZO ZTU-2500 3/4 BBb Tuba, Size:3/4, Key: BBb, brass lacquered, 4 front action stainless steel pistons, Leadpipe: rose brass, Bell size ...

The Mack Brass TU422 bore for its piston valves 1-3 is .689 and valve no. 4 is .707 That bore configuration seems popular, and is used by Packer JP179B Tuba and Schiller in a similar "Elite" model. The configuration is interesting to me as a weakening 82 year old amateur who wants to avoid lugging ...