I have both of the early MTH 5-Car Spine Car sets. The Item Numbers are 20-95035 (Delivered in 1997) and 20-95036 (Delivered in 1998). Both are listed as 1:48 scale and have an assortment of ISO Tanks, Containers and 48' Trailers. A little hard to find but they pop-up on Ebay every so often. A used, but in very nice condition, 20-95035 set recently sold for $175.00 plus shipping.
Chief Bob (Retired)