Here is you classic x frame used in full size chevy's from '58 to '64 as far as I know. Maybe in other GM product as well I am sure.

hereisyouclassicxframeusedinfullsizechevysfrom58to64asfarasiknowmaybeinothergmproductaswelliamsure.jpg

Notice how only those areas where the motor could spew oil on the frame are rust free. In fact still painted!

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