2004 zephyr...need help.

Side note @mykznme: the flashing graphic in your signature is pretty obnoxious. Thankfully it was easy to block.

Fugg man,its gone.
I put that shxt up back when MySpace was a thing. Probably before you were born..
now...does anyone else want to talk about bikes or am I just going to get peppered for asking questions?
This isnt FB or youtube.
Fuggin answer the questions or stfu...
There's really no need to be a dick.

Shxt,I'm Just trying to help a dood out with his first bike...

Clearly, the tank is from a ZR750H, which is a ZR-7S, Evidently, that part number, 51081-5439, was used on the ZR-7S from 2001 - 2005 (models A5 and H1 - H5). Since that could have been replaced along the way, the only way to know for sure what the motorcycle is, is to see the decal on the headstock of the frame.

Yes, By the sticker,.....it is technically a ZR-7.     ZR750H1...I believe the 01 after the sticker designate the year, which would be 1999 or 2001

The Japanese markings are very interesting. 

   The Zephyr 750s were ZR750C1 to ZR750C3.    Froim 1991 to 1993.    Again manufacturing year may be a year behind from marketing. .  The ZR-7 had heavily redesigned engine, rear frame, and swingarm, Brake calipers were different from the ZR-7 but intercheangable.  

Anyway, in general they used off-the shelf brake calipers  used acrros the board in other contemporary Kawasaki models.     Given the Zephyr or the ZR-7 sold in very small numbers, it is easier finding brake parts from the Ninjas 600s (ZX600)from the periods, ...at least in the US they were far more numerous. 
     
.....The rear caliper in the Zephyr I own, is from a Ninja 600, identical, other than the color which is black instead of gray. ,....Like Wookie and Nessism suggested, there should not be any problem rebulding them and finding parts,...even good used ones.