I can't tell without seeing both clutches, but might it not be easier to transplant the small spline hub into the larger clutch?
The other option is to go to the parts store if it is for an automotive application and see if they make a larger clutch with the smaller spline.
A real part store may help, such as a napa, or local store, not a chain store were the total IQ of all the people is less than the clutch diameter that your are working on.
Also don't be afraid to offer to pay for their time in helping you out. A $20 tip will make sure that you always get treated with respect. If you just take their knowledge and time and then go buy the part someplace else, you will never get this kind of help from them.