I installed the Edlebrock headers on my 96 4Runner a long time ago. Generally I think that the Edlebrock headers are very crude, but do work. Once I got the stock system off and saw that the exhaust ports in the head are larger then the inlets of the Edlebrocks I was very hesitant in proceeding with the install. However, the stock system was destroyed in getting it off so I had no choice, they had to go on.
I have some details on the install on my site if you are interested.
There was a definate increase in performance even without the supercharger. The headers seemed to unstuff the exhaust and the engine just felt more lively.
I had them on the truck for 50,000 trouble free miles then I decided to remove them and upgrade to the TRD headers. The TRD headers were about the same increase in felt performance of the Edlebrocks as the Edlebrocks were over the stock system.
I did have a lot of problems with the TRD headers at first with leaks and such. I had to design and make my own gaskets to solve the problem. TRD has corrected the short commings with their headers and I think that now they are the best choice for headers on this engine.
When you put the TRD headers along side the Edlebrocks you can clearly see the crude nature of the Edlebrock headers, but yes they do work.
It is my recommendation that once you factor in the cost, extream hassle of the install and the limited performance gain, stay with the stock system. If you must install headers, install the TRD headers and leave the Edlebrock ones alone.