Thanks to this thread, I installed a Polk Audio db840DVC sub, and it works. Wired in series, for 8ohm resistance. Getting some rattle when I crank it up, so I'm going to pull it back out when I have some free time to try and dampen the vibrations. Seems to be hitting the mounting brackets when the cone makes big movements.
I really advise taking some pictures of the stock sub with the brackets attached before you detach the sub. The brackets are not fully symmetrical, and the wire connections have to be on the same side as the original. I ended up having to pull the Polk back out to get the brackets right.
Also, I had to buy a pry tool to get the rear deck clips out because they were in so tight.
Nice to have some bass again!!!!