Looking for a little advice on the timing numbers I just pulled from my 73’ Duster (backfire issue)

Yes, I do understand. Do you? I will explain it for you.
Testing & research has shown that the optimum crank angle for maximum mechanical advantage [ MA ] of the force on the piston needs to occur with the crank angle 14-17* after TDC. Obviously, if the crank angle was 0, the crank would not rotate.
'Force on the piston' refers to the maximum expansion force from the burning mixture. At idle & low speeds, the toggling of the amount of ign advance that produces the highest engine rpm means that the above situation has occurred. At idle & low speed, the throttle is....throttled. Less dense, more distance between molecules, takes more time for the mixture to burn; hence the need for more timing [ time ] for the mixture to produce the optimum MA at 14-17* ATDC.

With retarded ign, the exh temp goes up. Also, the engine has to turn more rpm to make the same hp because it is now less efficient. Both factors produce additional heat which has to be dissipated by the engine's cooling system.