What type anchor do you plan using?
that has a lot to do with what roller will work. Notice Ross' boat has an unusual shape to the deck/topsides edge (gunwhale?) so he has to project the roller quite a bit further for the plow shaped anchor to clear than a conventionally shaped edge would require. You won't need nearly that much extension on your C30, but if you have a similar anchor you may need something to protect your deck from the long shank. My suggestion is to visit a good chandlery and let the salesman show you some options. I might also recommend you give Garhaurer Marine a call for their input. The have a lot of experience with Catalina yachts and produce a line of high quality, reasonably priced rollers.