The Delrin piece is part of the rudder control system on boats with the Delrin T-bar foot control and plastic crossribs. Up until about 1999 the Folbot rudder was controlled with sliding pedals rather than a T-bar.
I have not used this short-legged "T" with my GIIs but find it necessary for the Aleut and Yukon when using the T-bar foot control. Foot pressure on the T-bar can push the bottom of the crossrib forward, past the locking tab. Then the two brass pegs come out of their slots.
The short-legged T is a workaround to prevent this from happening. It is mounted, short leg up, through the plastic deck plate that has the slots. You may need to drill two holes. The short leg fits into the notch in the delrin ring pictured in your post. If the leg does not fit into the notch, enlarge the notch a bit with a file. The short leg then prevents the crossrib from moving forward.
Once the short-legged T is installed, the delrin ring must be removed to disassemble the boat. To accommodate folding a keelson that has a short-legged T installed, Folbot drilled a hole in the opposing deck plate. At least they did on the Yukon and Aleut. I'm not sure on the GII.
(Terminology for many of these boat parts is not standard as far as I can tell. I have read other posts that refer to the bottom frame sections as keelsons.)
I have not seen any factory workaround for boats with aluminum crossribs, which were introduced around 2003. My workaround is here:
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