and not only bought a couple of the Smoky Mountain urethane kits for Southern lowsides, but even found one of the old Rex zamac cast cars, which seems to be for the same prototype (and is a surprisingly good product for something over fifty years old).
Jace,
While I don't have much to add to the responses you have received about low side cars in general, allow me to point out that the Rex and SMMW S scale SOU gondola cars are NOT the same prototype. Inspect the ends. The Rex car represents series 55961-56560, built 1947 by PSC. IIRC, the SMMW car is a somewhat earlier series.
