1973 dart swinger fenders

'67 to '69 Dart fenders will fit with some modifications to the headlight/bezel mounting area.
It should be an easy fix if you have some rusty '73s to take that area out of and to compare. That area of the car usually doesn't rust or corrode, so you should be good there............
And of course the marker light area is different on these years and will require some modification.
AMD sells them new if there are any left in stock, but they're kind of expensive.........
The other option would be a set of '73 to '76 fenders which are fairly common so to speak, the pop up here for sale fairly often.
As for good used fenders, the '67 to '69 ones are usually a lot more expensive and the '73 and '74 are the same fender and the '75 and '76 ones have some small holes around 1/4'' or smaller on the side where the edge of the bumper sits away from the fender and it is for the rubber trim piece that bolts on there in those years.
It's hardly noticeable really or you can weld 'em up if you are concerned.
Side emblem trim holes might need to be modified/welded up and/or new holes drilled to your specific application.
(2 door and 4 door fenders are the same, BTW).
'70 to '72 fenders are totally different, with their bolt on fender extension on the front as well as the fitment of the other body pieces on your '73 would look wrong.
A common swap is to use a '70 to '72 Dart/Demon front clip including hood (all of the unboltable sheet metal including the bumper and brackets) from the doors forward.
I hope this helps...........
Tom.