Thanks folks: sorry if I was not clear - here is a picture of the current rim (looks pretty good in this shot but the braking surfaces are really bad):
The main centre section of the rim that you can see is a satin grey (almost like alloy rims), while the shoulders and braking surface are bright chrome. The Sun CR18 (and other replacement alloy or steel rims I have found) are either all satin or all chrome. Anyway, I think I am belaboring the point. If I do give up the interesting detail of the original rim I will certainly look at the CR18 polished.