some show him to have a heart part in there and others show totally different workings.
I agree with Dr. Frag,
The layout in his chest was pretty consistent throughout the 80s series.
As regards the 60s series, I have only seen 36 episodes recently, but Atom's heart is almost always visible when he opens his chest. If it is not, it is because of an obstruction, rather than absence.
Among inconsistencies, I have seen a stethescope, gieger-counter, and refuelling cable* in there; but the heart was always there, left of center.
*refuelling cable was used only for sharing his fuel. When Atom or any robot receives fuel, he always uses a (how to put this without being crude?

) female connector on his body to receive the male connector of the fuel source. I spent 10 years in electronics, and that is the nomenclature! the gas pump has a male connecteor, while the vehicle has a female.
As regards the current one, Atom's heart seems to be consistently dead-center in his chest.
Atom seems to lack the heads up display that the Terminators and Robocop have; perhaps it was cuter to put the communication stuff in his chest?
As regards communication equipment, manga #10 page 71 & 72 has him flip open the top of his head to expose an antenna, he speaks normally, and hears Dr. Ochanomizu (Elefun)'s orders!
:wahah: