I think the Dodge 413 and 440 were used when Dodge had Medium and Heavy duty trucks, back in the 60's and early 70's. I remember seeing Dodge 800s used as gas powered, city bus tow trucks and city tractors hauling around 40 foot trailers. I remember unloading 40 lb. boxes of lard from the Dodge Tractor's trailer into a cold storage, during my Univ. days. These tandem axle Dodges were the size of gasser Louisvilles L800s.

I also remember seeing Chevy C70's (medium to heavy duty) equipped with 366 and 427 big blocks. Around 1970 the local newspaper used one of these (C70) 427s to haul newspapers from my city to small towns in the country. That 427 would move with a full load, and the noise it made was a glorious V8 sound. The chevy big block, truck engine I believe has some differences compared to those used in light truck and car applications.

GMCs used variations on their 305 V6, which was a well cooled, heavy nickel content block used in P/Us to MDT. You could get bigger V6s in the GMC line in displacement up to about 470 something.

International, back in the 60's used 304, 345 and 392 gasser V8s, all using the same high nickel content block, just with variations on bore and stroke.

I used to drive a 460 V8 in an E350 dually , cube van and although I thought the world of the 460, I'm pretty sure this engine was just set up for light trucks, up to the E350 and F350.

The built Caddy, bow tie 502 and blue oval 460 you refer to, I don't think would be heavy duty enough for Medium duty and Heavy duty service.

I think the MDT and HDT, Ford 534s, Internationals, GMC and Chevy big block truck engines met different specifications than did the car/light duty truck engines. They were for the most heavy engines,with lots of meat. Not quite built to Diesel standards, but beefier than car/light truck standards. In a MDT/HDT, these engines are having their comparatively low revving necks wrung, and have to be built to withstand this kind of severe service.

Just my speculation for the most part.