The RSR Aluminum crossmember was forged and made from a stronger alloy, as opposed to the more common Aluminum casting. Also, the RSR crossmember has 2 bolts holding the metal-straps to the body (you will note if you look carefully). The two pieces don't even look the same... Porsche p/n 911.341.013.03 - If you want to see this part installed in a factory 1973 Porsche 911 RSR, look here https://pbase.com/slidevalve911rsr/image/53887330