M_Boats: Finding the center board pivot pin

I was working on my new '78 M-23 and am pretty sure I found the stop pin for the center board, but I am having issues locating the pivot pin. I have been stripping the old bottom paint but I do not see an obvious dent, circle you name it for the pivot pin. This was easy on my M-17 since it has a pivot bolt and nut recessed into the keel. So do you sailors have a suggestion or experience locating the pivot pin? I want to drop (not literally) to board so I can take it to be blasted. Thanks is advance. Robbin