1973 Dodge Dart Sport 340 { Trades? }

Dan, very nice car.
I looked over your ebay ad but didn't see any mention of dealership documentation for your car. That might help get the $$ you are looking to get for the car.
As for 73-74 Dart Sport GSS cars, here is my take on that subject. I feel confident in saying that there were Dart Sport GSS cars built. I have two ads I believe in my collection mentioning the cars. One is as late as June 73 which in the magazine world would translate to mid year 73 production. The ad states something to the effect of "Speed shop installed". The reason Grand Spaulding stopped making these cars was due to federal regulations that prohibited them from modifying cars that were new. At the time, a bypass to this law was to have an off site "shop" do the performance upgrades. I think the basic difference might have been just the way the sales ticket was written up or maybe the extra parts weren't able to be financed with the car at the time of the final sale. Not sure on this. I don't believe that an outside shop actually did anything to the car, they might have just moved the car across the street to another division of the dealership. The car in MCG from Beloit WI is an example of the cars in question, plus I have seen/heard of at least two more that I believe were GSS cars. You have to keep an open mind with regard to GSS cars, it's not a cut and dry option list. Not all 72 GSS cars came with a Paxton , not all Dart Sports came with a Paxton, some people liked/wanted the six pack, or, maybe they stuck with the 4 bbl but had other performance upgrades done at the dealership. I've never heard it talked about or seen it advertised but I think of this as a sort of stage 1, 2 or 3 type performance level with these cars, whatever the customer wanted, whatever he could afford. That's not to say every hi-po car sold at GSD should be considered a GSS of sorts, even though they were all dyno tuned, but any level of "beyond factory" upgrades to me make it something noteworthy.

Again, this is all just my two cents, based on years of research on my end.