why do some 440 hemi 4sp dana cars have finned brake drums and others don't?

I believe it is because cars with front drum brakes have 11” rear drums, which are finned. Whereas cars with front discs have 10” rear drums, which are not finned.

Because finned are stronger & less likely to warp, unlike earlier which were not finned & had those awful coil springs. Same reason they started putting fins on the inside of rotors

Those springs wrapped around the drums were not for heat dissipation, they were anti-chatter springs.

See: as the drum turned, air would flow thru the springs coils, which were in contact with the drum, thus acting as multiple heat "fins".

When we turned drums back in the day there was a “device” wrapped around the drum to stop the chatter. Same idea as the spring.
I also have 11” drums finned and no finned so the size doesn’t mean finned. Chrysler did make a few front drums finned and back ones not.

.
All the aftermarket ones I saw were finned mine I blasted and [censored] them when I broke a stud as I had them off

where did you find aftermarket find drums?

Advance, I also checked Auto Zone and the others but they had Canada or USA at advance it is luck of the draw as to what they have in stock
Also, Check Rock Auto.

Wagner BD60187, 11", think I got them at Auto Zone.