The tail cow and "wedge" are the same but the frames are different. The mounting for the side cases use the same side Z racks too but the tops where they mount are wider apart on 4V Ks because the bottoms of the racks at the peg plates are pushed out to accommodate the backs of the peg plates being wider for the hump where the paralever final drive shaft housing pivots in the middle.
On a K75/K100 the Z rack mounting point is below the middle of the frame. On a 4V K bike those same mounting points are out to the side of the frame.
K75/K100 frame:

4V K bike frame:

This is why there are two different Reynolds Racks for 2v and 4V K bikes.
However, it is quite possible to retrofit a K1100LT tail rack to a K75 or K100. BMW even offered a kit do do so:
https://www.realoem.com/bmw/enUS/showparts?id=0573-USA---K569-BMW-K%2075%20RT%20(0565,0573)&diagId=46_0319You'll just need to experiment some to figure out the correct bolt length and spacer width.