I'm not sure I understand your question. Don't the ratios strongly suggest that it's the Yosh 320-506-0000 wide ratio transmission? As I understand it, there's an "A" mark on it somewhere, possibly on each gear. Or are you trying to determine who made them for Yosh? Was anyone else independently making gixxer transmissions? VERY pricey.
FWIW: My analysis indicates that the K5/K8 OEM transmission would have smoother spreads if 1st gear was 42/16. But that's unlikely to ever be available.
I would like to if this really is Yoshimura gearbox as the ratios suggest. I could only find some markings on the gears (e.g. 104 2R).
I'll need to take a closer look at the gears...
but with some missing small bearings on the shaft ends and an iffy looking output shaft oil seal (both should be minor items).
The main issue is do you need a wide ratio transmission. Note that even though it's referred to as wide ratio, the spreads are much narrower than the OEM ratios. The overall spread (1st to 6th) is 1.839 vs 2.019 for the OEM. Your pics don't seem to show it but I'd be checking for mods like drilled gears, ISF, or undercut dogs.
Definitely not need one, more like nice to have part.
I got it for a good price, not much more than a used oem gearbox.
I think this should be pretty much spot on for the track I usually go. Stock 1st is a bit too short and 2nd too tall.
Do you have any idea where the weight reduction comes from? I'd assume that the bearings are the same. Or are they ceramic? I guess that the gears could be undercut or the drive shaft could be drilled.