They don't come this way, so some prep work is involved. I always soak my FUD/FXD parts in Bestine rubber cement thinner for about an hour, then carefully remove them from this bath with latex gloves and long tweezers. From there, they are rinsed in warm water, and dried on paper towels. Once dried, I spray them with Tamiya NATO Black acrylic. Any brand should work, and color is a preference up to the modeler. I like NATO black because it's as close to black as it comes, without actually being black.
After the paint dried, I hit the journals with some fine graphite dry lubricant, which I always use for trucks, in any material, and installed the Fox Valley Models N scale 36" wheelsets. (.540" axle length)
The trucks roll freely, just as good as any commercial truck, as you can see below.
My buddy Chris was an early adopter of the Marsh Creek Trucks, and you can see his layout in progress below. You can't see them, but the Marsh Creek trucks are on the flat cars in the video. Chris is a phenomenal builder, and it's a source of personal pride that he's using my trucks.
Go build something awesome!