Lockforward

My current reservation, booked thru NW but on DL metal has me returning from EZE on Mar 21 to JFK. The availability looks like J9 D9 S9 I9 Y7 B7 M7 H7 Q7 K7 L7 U7 T4 , and I am on a L class ticket. I currently do not have an assigned seat, and when I go to delta.com It shows no available seats. As a NW Gold, should I be able to select a seat since it looks there are seats available? If so, what would be the best way to do this? How's my chances of getting bumped off this flight?

Thanks for your wisdom!