John, I can't answer your question right off on whether ballast was used in SVRy's plow, but if I run across a weight for it, which I think I may find, this could be a clue. If it weighs substantially more that a caboose plus a reasonable guess for the blade likely they added some scrap iron on the deck below the car body. Also Garrie Tufford called me to confirm that it is his opinion that in the photo he did the write up on posted above it does show the snow plow behind the mystery caboose. In fact he said he was going to write a new caption that clarifies this.