The black plastic pushbuttons tell us it's a 68-9 B body radio that someone has swapped the 68-9 Barracuda chrome bezel and lense on to.
The other obvious sign will be the location of the mounting stud .
It will be on the back of the radio for the B body, and on the bottom cover plate
for the A bodies , and rallye dash and non rallye dash A bodies used two diffrent locations , note the DV(Dart Valiant) and B(Barracuda) stamped in to the bottom .
Had it been a correct 1970 Duster 340/Dart Swinger 340 it would have had the same fat chrome push buttons as found on the 68-9 Barracuda and Valiant. The thin chrome push buttons are unique to 68-9 Dart .
I see alot of these "Frankenstein radios" where someone has taken 2 and somtimes 3 diffrent radios and tried to make something that fit their application.

Greg