Bringing up this old thread because it's the first one I hit, searching for past web posts (at large, not just on this forum) re "Selmer tenor necks Keilwerth."
I did not have the same finding as reported earlier (which, who knows, may have also changed for the posters in 14+ years).
I have a Bundy Special that I did a big experiment on (not the bore, just the hardware other than the bore) because, worst case, I would probably end up with a Keilwerth that, after experimenting with necks, I would like better than or as much as anything preceding the SX90, maybe even including the SX90. That was the goal.
I finally (last week) picked up what seems to be a lacquered SX90 neck, and spent a few days playing (in the Bundy Special) the original Bundy Special neck, a Selmer Ref 36 neck, the (putatively, by me) SX90 neck, and a Crescent 1 (my line's) neck.
Long story short, they all matched. BUT, each had differing results not only individually, as far as consistency of response over the range of the horn, but relatively to each other in terms of comparing intonation, tone and response not just across the scale, relative to that mouthpiece on that neck on that horn, but between necks -- i.e. what was the case in comparisons (e.g. "this one's lower end plays easier and better than the other") with one mouth could completely reverse with another mouthpiece. The mouthpieces: Vintage 8* metal Link refaced by me, Stephan Kammerer "Omnis," Ponzol II-V-I, and Ponzol M1 refaced by Sakshama.
I'll make a follow-up post with sound samples if I can ever get around to it, but my basic finding is that not only are modern Keilwerth necks compatible with old Keilwerths such as the Bundy Special (probably the inverse also applies), but Selmer-compatible necks (which the Crescent 1 is, and the Ref 36 is), are also all potential candidates.
Probably a challenge in testing this is that necks made for Selmer have a much smaller tenon sizing than Keilwerth, and when you're adapting with teflon tape, you're not going to get a true comparison -- your neck is going to be loose and rocking. My surmise is based on the Crescent 1 tenor being Selmer compatible (acoustically, which it is, and vice-versa) but having a tenon almost identical to both the original Bundy Special and (putative) SX90 neck, which are also nearly dead-on with each other in sizing, which allows me to make an educated guess as to how much response I'm missing when I play the Ref 36 neck with teflon tape to adapt its sizing (its scale was tonally uneven, sort of as if the keyheights were all very off, but intonation was great, and response was in some ways an improvement over all the other necks, but I only played that neck with the vintage Link, during the first test session, i.e. not with the other mouthpieces, so the comparison might have changed or even been the opposite with the M1 that I felt was the best mouthpiece for the other necks).
Anyway, my finding is that Selmer necks ARE compatible, and maybe of particular interest to some Keilwerth owners when the owners find their current necks to lack nuance, subtlety or sensitivity -- or, put another way, to have so much power and forward, out-front drive that more subtle articulations are sort of discouraged or seemingly resisted by the horn. BUT they will require a very significant tenon expansion for their ultimate match/form/performance to be unveiled.
Anybody who doesn't believe me is welcome to try a Crescent 1 neck (which has a Selmer compatible bore). Just pay me for my time and the shipping, because I'm not made of money. Sadly.
