I just refinished a set for my 73. The black around the outside with Argent in the center is correct. When you refinish you need to take the cap apart. You can polish the stainless with buffing compound pretty nice. If there is scratches you can sand them down by hand using 600, 1,000, 1,200 grit them buff them. It is pretty much impossible to remove dents since the cap has two layers of material you cannot get inside. The center plastic emblem you can also polish. DO NOT pull the foam pad off the back of the plastic. It might pull the paint off with the foam.
There are actually couple different versions of the cap for 14" and 15" wheels I believe. There are also two different shapes of openings for the valve stem. One is football shaped and the other is oval shaped.
NPD sent me the incorrect spray for the dark area but I used anyway.
You should scuff the areas to be painted with 600 grit or Scotch Brite to make the paint stick. You need to mask off the shiny border around the openings front and back then spray the flat black around the outside of the center. After spraying black and dry then start masking the shape of the Argent are. Just follow the tangent of the radius around the center. Spray about 3 coats of the Argent and when dry remove all of your masking. Peel off slowly the paint does not like to stick to the Chrome on the center part of the cap.
It took me about 6 hours to mask and paint 4 of them after I had polished and prepped the center part of the cap. I also cleaned up the fasteners before assembly.
When you put them on use a big rubber hammer or dead blow with a towel taped to the face to prevent damage. Here are some pics of mine. The all black centers are 70 or from Mercury. You should have the Argent in the center, see brochure for 73.
I make my own narrow masking tape for doing the tight radius turns on both hub caps and on consoles and dash panels. You can get a plastic cutting board found in the sewing area of department store and I use a rotary scissor to cut with a straight edge. That was I can cut any width I want. I used 1/8" to do the layout of the edge and then came back with wider to cover the large areas. Last thing you do before spraying is go around and press tape down good. Some people will spray clear on first so if there is any bleeding you cannot see it. Not needed on the covers nobody going to get down on knees to view. If you are painting the black on a hood then doing the clear first makes a cleaner job.
I went through 11 caps before I found 4 decent ones. Several had the fake lugs broken off from tire guy thinking they were real. One had all five twisted, he was a real dummy for sure.
The trim ring part of the cap had a sanded finish after polish. You can do this while on the car spin the wheel and hold sand paper against the surface. Sand stops about 1/4", 6mm from edge.
Last three I got at a swap meet were $20.00 for all three.