There is actually a section in the body manual for the 964 that gives instructions on how to prepare a chassis to the RS specification which includes, among other things, seam welding. I found that the seam welding in the manual was minimal and generally concentrated around the rear suspension pick up points. I ended up seam welding every panel in the chassis, similar to the approach Riccardo took with the GT3RS cars which were later outlawed by the ALMS. I put 3lbs of TIG welding rod into the car, so it doesn't add much weight.

 

Thanks