Dave,
I am able to answer your questions in part.
1. A B&H Imperial in the 11" bell era is the same as a Besson New Standard. I "think" that they switched from the medium shank receiver to the large shank receiver around the time of the Sovereign introduction in 1974-ish. This also coincides with the intoduction of the Wick 4AL as the standard mouthpiece on the Sovereign. Most of the medium shank New Standard/Imperials came with a Besson 10 (a truly abominable mouthpiece). Thank goodness they also came with the tenor-to-medium adapter. I used a Bach mouthpiece throughout my university years (1969 - 1974).
2. Yes Imperial and Sovereign were produced in parallel at least through 1980. Generally the Imperial/New Standard (at least in the medium shank era) had better intonation than the Sovereign. There was some resistance to the Sovereign when it first came out due to the wild intonation. For instance Trevor Groom would not play one and gave up his relationship with B&H/Besson as a result of this. Also, not everyone went for the Sovereign 967 sound initially.
3a/b. The Sovereign 966 definitely replaced the Imperial/New Standard. It differed in bell size and leadpipe from the 967. I am told that the 966 was a 967 with the 11" bell and a diffferent leadpipe than the 967. It was more "Z-shaped" and less "S-shaped" with a more gradual taper. The 966 was first produced in the "soldered to the bell leadpipe" era and had metal valve guides. I believe it evolved into the 968 when they switched to floating leadpipe and plastic guides. (I am a little fuzzy on how this all transpired).
4. I think I answered this in #1 above. AFAIK, the "receiver" was converted on the early large shank Imperials, but the leadpipe didn't change. Many earlier Imperials/New Standards have had their receivers replaced as well.
An aside note: The introduction of the Sovereign 967 with its change in sound and intonation issues, combined with the Blaikley patent running out, created a huge opportunity in the American Military bands for Willson. Look at the specs on the Willson 2900, and what you see is something akin the Imperial/New Standard. Dr. Bowman, who had been playing an Imperial, was the catalyst for bringing the Willson to the fore in the "American style" wind bands.
Last edited by daruby; 07-15-2020 at 12:16 PM.
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band