Here' something I've been working on for about a decade and finally finished (not that it couldn't use more work). Its a rather obvious combination of the Beer Wagon and Boothill Express from Monogram. Both source models were incomplete eBay buys.
The marble effect was an experiment that turned out well. I did it by brushing water over the primer and then dabbing/dragging in little bits of dilute black acrylic. Fortunately, "marble" allows a lot of leeway. I've used a similar technique to fake wood grain.