Congratulations! I have exactly the same model with the original leadpipe bow and large receiver ("pre war" as I know the full history of mine).
I was at Alexander im Mainz just recently and could play the current 164 gold brass model side by side with mine. The old model definitely plays on par with the current version!
I know that you're a far more advanced tuba player than I am but I can only encourage you to test a mouthpiece similar to e.g. Giddings Szentpali CC (I have the titanium version) adapted to the large shank or the more cost sensitive option "AMH Paul der Große PRO" from Bob Tucci which almost plays and sounds the same and fits just fine at the end of the shank. The sound over the whole range is just amazing, this is the feedback I get. Those Tubas seem to like large and light mouthpieces and play up to the F-Tuba range easier than my F and Eb instruments (of course not as flexible). I was lucky to attend a workshop also in 1:1 with Stefan Ambrosius who gave me valuable hints to master this Tuba and having him saying that he likes the sound very much (adding that one has to invest in practicing especially with the old Alexander Kaisers). Intonation is totally steerable with 1st and 2nd slide and fully chromatic (I use the 2nd slide ring as thumb ring and Meinlschmidt slide oil on both slides). Even low H (B) is available als usable false tone (you just need this one) with 1st valve and 1st slide fully out as it is on Stefans 197/2. 1234 all in is low Db, 1234 all out is C. 4th is always as far out as possible. They changed the 4th valve "reserve" for the newer 164.
Sorry for this enthusiastic post, but I was really triggered by the picture :-)
Best regards
Thomas
P.S.: I have a PT50+ with enlarged shank done by a professional local workshop which also works quite well. But I do not need it anymore as I have both the Szentpali and the AMH.
I took a photo of "grandfather and grandson" last month in Mainz
https://photos.app.goo.gl/jedfkr4AnRZ3QxjE6
one more addition: You had the 17 inch Besson BBb, right? I have the similar New Standard model Besson 226 as 3-1 comp which gets restored to an optimized new condition by a german tuba builder. We seem to share the same tuba preferences :-). And I must add, that both tubas are very cost sensitive ("value for money") even including the restoration work.