Kurtk. O'DAY didn't use any chain in the centerboard pendant, but for a few years they did use a centerboard pendant that was half stainless-steel cable, half dacron rope. There was splice where they joined. Most of those have by now been replaced by all rope (polyester double-braid usually). BrianS has good information and that was basically how all O'DAY K/CB models (26' and under) were rigged (except 1971-75 O'DAY 23 and 1975 O'DAY 25) as far as I've heard and seen. I've added a picture below of the pendant attached to the CB, it is from a 26, but it still shows pretty much the common setup. I'd be a bit concerned about that large thimble and splice shown, it may jam things up, but if it worked for that boat..... still, it looks big to me.
The 1975 model of the 25 had a different setup, with the CB pendant coming up in a pipe in the middle of the cabin and had a crank on that pipe to raise/lower the CB. These too used cable originally with no chain. The pipe was under the table.
Anyway, no chain was used from the factory, but who knows what a previous owner might have done? <GRIN!>