Replacement for 1970 Besson Euphonium
Based on your size discussion I would consider the following:
1. Besson 968 - should be similar in physical size to your 1970 Besson (11" bell, similar overall), but uses a large shank receiver.
2. Yamaha 842S - Has leadpipe mounted low on bell and the third valve slide is very close to the outer branch to make the reach to the 4th valve very manageable. Feels much smaller than a 642S.
3. Willson 2900 - Euro shank, smaller bell horn, generally feels "smaller" than a Besson.
4. Get your 1970 Besson rebuilt by a reputable group. (Expect for it to be gone for at least 6 months). Rent or purchase a used Yamaha 321 to hold you over till you get your Besson back.
Doug
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band