what is original, what is rare option, what is not?
The VIN on the door says that it wasn't a super 6 (engine code C), and that it was built in Michigan...
LH23C3B109798
Make
L = Dodge Dart / Demon
Price Class
H = High
Body Type
23 = 2 Door Hardtop
Drive Train
C = 225 105HP(net) 1-1BBL 6 CYL
Model Year
3 = 1973
Assembly Plant
B = Dodge Main, Hamtramck, MI, USA
Sequence Number
109798 = 9797th Vehicle
The 8 3/4 shouldn't be original either. Last year was '72 in A-bodies, and it shouldn't have been in a /6 car either. That said, this is a very early '73 car (8/'72 is the first month of production for the '73 model year), and Ma Mopar has been known to send leftover parts from the previous model year out the door early in the production of the next model year. The 742 center chunk though is definitely not original, and more than likely neither is the 8 3/4. I just wouldn't say it's impossible. However, if the car got the full towing package (A35) it should have factory disk front brakes, which would mean a BBP rear axle, which would mean no 8 3/4 regardless. That's one thing I have
never seen, a factory A-body BBP 8 3/4.
The map light isn't that rare, the rear defroster is a little more rare but not some crazy, unheard of option. The dual mirrors were not available in '73 for a Swinger, at least according to the factory options book . However, you could get dual mirrors on a swinger in '72, so that may have been a left over. Or added later. The remote trunk switch is probably a later add on. Of course, without seeing the fender tag or buildsheet it's impossible to say for sure what may have been added later.
Here's some info on the towing package from the factory literature over at hamtramck-historical
http://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1973/73_Dart0022.jpg