When I buy zincs for Lady Jo, I buy the set that is two fround disks kind of like flying saucers. I use one half or one of the zincs on the port side rudder cheek and the other half or disk on the starboard side rudder cheek.
So far so good.
I have not seen a good place for any zincs on the keel.
I own a c-26 I just re did the boat and didn't find any zincs at all not even on the outboard. It has always been a fresh water boat do I need the zinc?
Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.
--Mark Twain
EE has an under hull flat zinc about the size of a Hershey bar (mmmmmmmm, chocolate....) -but much thicker- under the stern berth area. The ( heavily sealed) bolts that attach it are also the terminus for the rig's ground wires.
Eh, not good ones. I dug a couple a pics that happen to show the zinc and connection. I emailed them to you with some arrows drawn. Maybe you can zoom in enough to see it.