Phil's right. Gathering all this is not easy. I looked awhile for another OP concerning later models, and the two "looked" more alike than now. Without going back to chase numbers, same front axle capacity, rear axle capacity in E350 increased but still notably less than E450, rear axle tracks much closer to equal. I didn't look at driveshaft etc, but the two basic FRAMES are different which Phil alluded to. As I recall, E450 is a "deeper" form factor of material that is both thicker and tougher (higher tensile rating). FYI and in the interest of accuracy/truth in advertising, the Ford frame specs are higher than Chevy.