There's a chance the cams are the same.

Also, because an engine is bigger doesn't mean it has "larger" cams - for example, duration of 3.5 cams is longer than those of a 4.5 (m116 vs m117). I would assume the same to be true of 500 vs 420 cams, since the 420 has less displacement, it has a longer duration to compensate for that.