I think that "10.252 Plate Instrument panel trim" is the instrument panel with the radio opening. It only shows different part numbers for AC/non AC and standard/custom trim (the woodgrain on custom interiors). No difference between radio/no radio which makes me believe that the instrument panels all have holes for the radio in them.

9796880 might very well be the radio delete plate (called "Plate, radio opening cover/accesory swith opening").

3903481 must be a cover to install instead of the speaker (called "Plate, Speaker opening cover").

If you look here, the 1969 radio delete plate is shown in the picture, the number references seems to be wrong though
http://thefirstgensite.com/library/partscounter/illustrated/interior/dash1.html

I'm no expert on this so I'm not saying I'm right, just trying to interpret the manuals the way I think is right.

Ronnie Stensson
Sweden