Shane,
Congrats on the new ride. You will really like the Cobra too.
I have both an upper pulley (2.93 Lightning) and a lower pulley (6# Metco) on my 03 Cobra. Unlike the Lightning, the Cobra requires extra bracketry (about $200) to use the lower pulley, so it is a somewhat more expensive mod than on the L. In addiition, I installed the larger Metco alternator pulley (another $55?) to slow down the alternator on my car.
I look at all of the 03-04 Cobra's at car shows I go to, and bt that I see that most guys have replaced the upper pulley only (if at all). An upper only on these beasts can yield quite a bit of power with a good tune. You will pick up a lot more torque with a lower pulley too, but the RWHP won't change much.
Same as the L, go for a Chip(tuner), pulley, and filter first. Have fun with it.
Lightning Bob