Here are the inspection ports on my boat
As a fellow DS II owner, I think I know what you are talking about. the 2 deckplates/inspection ports located at the forward end of the cockpit sole, used to access the bilge under the cockpit of the DS II as well as to access the pivot bolt on 1971-79 models. I will include a picture of this area on my boat. They are standard 4" deckplates, original may have been Beckson, but more likely was another brand. I bought a pair of Beckson 4" screw-in ports from Rudy at D&R, I did need to slightly enlarge the holes in the deck to get them to fit (carefully used a rasp)but it was well worth replacing the original plates! The thread is very fine on the originals making them hard to open/close, the Beckson ports have a coarser thread and screw in/out much easier, plus they seal better.