Having retrofitted my '04 with the LED tails, I can tell you that it should be pretty simple. (I know it's the opposite operation, but in theory all the parts should be the same.)
That socket in your picture there is the same one that I have. When I took my bulb out of my '04s, all I did was plug the existing socket I took from my '04 tails and snapped it into the LED wire harnesses from the tails. IE, they are "plug n' play". You shouldn't require anything more than you have now, the bulb should fit right in where the LED connector did. After that, just plug it into the truck's harness and you should be golden.
If this does not work, it might be possible that you need to order up an '04 socket, which you can get from partznet (see link on top of page) but these sockets should all be the same.
So in a nutshell, try plugging the proper bulb into that socket you've got and see if it lights up, it should.
Good luck!