Bob, what material were these made from, Black Detail, FUD painted black, White Detail painted black? They do look very nice and I imagine that the varied depths of the design helps to hide any raster marks that may be present. Thanks for sharing.
You can buy them in other materials than FUD, but FUD is all I would consider. You gotta soak them really well with Bestine to get rid of the wax, and that means overnight, and even then use a soft toothbrush to gently get all of it off. You'll know when it's all gone because they'll get totally opaque. If your flat paint is shiny after you paint the part, you'll know you didn't get all the wax removed.
I used Krylon Cammo Black, which is an ultra flat paint to paint mine...just because I had it on hand.
Although they look a little rough (emphasis on "little") when you inspect them before painting, it goes away after a thin app of paint. I used the recommended Fox Valley wheelsets for them and I am completely taken with the brake hangar details, which simply could not be accomplished with a single piece injection molded truck sideframe.