Create, not re-create!

It might be more practical to build reproduction equipment that could be used in regular revenue service. Build a parlor car for premium service or charters, much like the Nomad, etc. at the D&SNG. Build a couple of San Juan look alike coaches but put in 40 seats. Build or rebuild an RPO with a wheel chair lift in the door for handicap service. Build a baggage with water tank and pump for fire service. Since you can also transport back pack pumps, shovels, etc., it would be more practical than hauling the rotary tank.
As Boris said, all you need is mucho dinero. Proper trucks would be essential and not cheap. Car body costs could be figured by contacting either the D&SNG or Marty Knox at the Huckleberry. They built a gorgeous combine a couple of years ago, using traditional construction.
Once all the other problems are solved, it might be worth considering a few years down the road. Rather than building more ugly passenger cars, spend a little bit more and getting them looking "right" might pay off in the long run in increased charter revenue.