The setup of the pivot pin on the O'DAY 20 Centerboard changed a couple of times over the 1973-78 production run, Rudy at D&R should know what the setup was for 1975, but although he is a great source of knowledge, some things he is not sure of. The 20 was also built at 3 Factories (Fall River, MA, Costa Mesa, CA, and one in Kansas) so it is possible that they switched setups at different times?
When calling Rudy at D&R, remember that D&R is literally a "Mom & Pop" shop, it is just Rudy and his Wife. They do their best, but unfortunately may get "snowed under" at times. Obviously, mid-to late Spring, they are VERY busy as we all get our boats ready and suddenly realize that we need parts before launching and despite out good intentions to order them in the Fall, we forgot and need them NOW. It is the curse of Spring, and all parts suppliers/manufacturers get busy.
The 1973-74 model had a pin inserted from one side, so you should see some kind of plug/putty spot on one side of the keel covering the pin access.
At a later time, (maybe 1975?) the setup was changed to have 2 metal "hangers" that held the CB pivot pin, these will have a stainless-steel plate on each side of the bottom of the keel, those plates are attached to vertical stainless-steel plates that go up into the CB slot one on each side of the CB, the pivot pin is metal on those and attached to one plate (I think) with a short tube on the other plate that the pin fits into.
I think the last boats built (1978) may have had the 2 fiberglass wedges, held in my a pair of Stainless-steel plates, with the wedges holding the pin in place. Just like most of the other O'DAY K/CB models.
Here are some pictures of the setups:
