For more modern altos, the "Buescher" BU series and the Selmer Bundy II should be the same animal: a student horn, probably built in China or Taiwan, using the basic "Mark VI copy" for the design of the keys.
Looking back, I see the 1963 - 1965 Bundy saxophones as Bueschers with somewhat altered key designs. My first beginner alto was a 1964 Bundy bought in 1964. More than 40 years later, I got a Buescher 140 Aristocrat, and it seemed to be the exact same animal, right down to the sharp high A and flat low D, except for the nickel plated keys and the absence of Norton springs/Snap-in Pads on the Bundy. Of course, a sharp high A and flat low D are typical problems in all sax designs due to compromises in placement of the octave key pips.
I have played a mid-1960's Signet with the S brace, and it played exactly like my Buescher 140 alto minus Nortons/snap-ins.
I have also owned a late True Tone alto (with front F and the usual hissy high A). I have long suspected that the 1964 Bundy has a TT neck with a smaller top octave pip hole to alleviate the hissy A. There seems to be a lot of disagreement here about my next statement, but I will stand by it until someone (Jicaino?) proves me wrong. The Selmer Signet alto of the mid-1960's with the brass keys and the S brace seems to be the same horn as the Buescher 140 with the best Buescher neck. Some here insist that the Signet is based upon the Buescher 400 alto, but none of the telltale signs are present: no large bell flare, no "inside RH" bell keys, no underslung octave mechanism, and no nickel keys (which were common on post-TH&C 400s). It is true that the last 400s had LH bell keys like the Signet, but so did the Bundy and Aristocrat 140.
So, it is my theory that Selmer took the Bundy with nickel keys from the Buescher 140 with one of the earlier TT necks, and then they took the Signet with brass keys from the 140 with the best TT neck. This gave them 3 levels of instrument: Bundy, Signet, and Mark VI.
Ah, I see in the thread cited above that Jacaino agrees with my neck statements on 1964 Bundy and Signet altos.
Sax Magic