I don't know about the C30 but the C34 and other models use a shallower rudder on the wing keel. If that's the case it would be much easier to try a rudder mod before attempting a keel swap. They are too light and under ballasted. Catalina always adds weight to the wings to keep them approximately as stiff as the fins. By the way he ended up ordering a c36mkII with a wing keel which keeps many more cruising options open in NG Bay and beyond especially when you start out up in the shallow end of the Bay.
Someone has to stick up for the fin keel.
My 42 has a fin keel. I've sailed both, although the other s were not Catalinas, I was sold on the fin keel. I asked Catalina this same question when I went on a factory tour prior to attaching my keel and was told that if draft isn't a problem he would stay with the fin. During most of the year my boat is on the Columbia River, and being able to point as high as possible is great. Being able to rock or back out of a mud grounding works for me .