A radial master cylinder has the piston and cylinder turned 90 degrees compared to a conventional master cylinder. IE The cylinder is perpendicular to the handlebar.
Looks like 03 and 04 ZX6R used a Nissin conventional, non-radial MC
It is simple hydraulics and if the bore and stroke of the cylinders is the same it will work.
Complicating all this is the distance between the lever's pivot point and the plunger that pushes into the cylinder. This inter-axis value is the second number in radial MC specs - for example 14 (bore) x 19 (inter-axis). As that value increases, you are decreasing your sensitivity and increasing your brake power.
I am hoping against the odds that it will work. In any case I would rather do the engineering first rather than bolt it up and then find out that I need a new MC
Just went out and looked at the Versys a bit harder and it is a Nissin 14mm bore MC
Now just to find the stroke of the Nissin and specs on the ZX6R