J-body w/ headers

I hate to be the dumb one in the group but what is the J-body? i have a 2003 Ls Auto ecotec and i dont know if i have the "J-body" or not. I want the ( http://rksport.com/prod_detail.php?prod_id=020910026&view=detail ) header from Rk sport but i dont know if this is a good price and if it is worth it. I want to do headers back. Do i need a cat-converter? one last thing, what kind of system should i get? keep in mind i dont have that much $. thanks

a jbody is the body type which consists of the cavi and sunfire, then theres nbodies which are grand ams aleros and so on, fbodies camaro firebird.

oh ok thanks