Viking with a Hammer
Chet, the pics you posted are apples and oranges. Those two trucks are different generations and of course those frames are going to look different. I've never seen a frame under a cab only fleet vehicle that differed from its equal duty pickup bed equipped version.
Ford has used a different frame and rear springs on chassis cab trucks since at least 2017. IIRC, Dodge as well.
Modern boxed frames suck for 350 and heavier service trucks, with service bodies or flatbeds.