I dont think it is even possible to use a four link on the factory subframe withou adding structual rigidity. But try this link, this is where I bought my four link. http://www.autoweldchassis.com/ls.ivnu If you give them a ring they might be able to hook you up. Prices are very reasonable, The lowest I have found.
Try Martz as well. Here is a link....http://www.martzchassis.net
This is the 4 link i am installing. When are you jumping into it ? If you have not done it by the time i do mine i can give you pros, cons and pictures !!