I do not have a Sport model with a Argent grill, but I just went through this painting my WW grill on my standard 1970 EB.
I painted the WW first, then taped the grill and painted the body color.
If I were to paint another, I would paint the body color first, then tape off the outside and paint the grill color second. IMO, I think it would be easier to tape the outside, it was a pain to tape the grill. Just hit the overspray areas with some 320 before you shoot the second color..
Make sure you use the 3M fineline "blue plastic tape" for the paint demarcation line. It's $20 well spent.
John