We did this replacement two years ago on our C&C 35 MKIII, We replaced the wire rope splice with New England ropes T-9000 low stretch Dyneema core. Could have used Sta Set also.
As far as the sheeves, we went down on size diameter on the lines and have had no problem fitting in the old sheeves. I would replace the sheeves the next time you bring the mast down and it is a fairlry simnple job.
BTW. we have noticed raising our main to be so much easier with the all line halyard.