Ted,
According to American Refrigerator Transit (Maher, Michelson, Semon) this would be the closest series to the MTL car. (Not exact match since the MTL car represents a FGE prototype)
RMDX 325-464 built by PC&F 1962 56'10" 70 ton 140 cars
These cars had 20 inch cushion drawbar so that extends the outside length.
There is also earlier series that are close to the MTL car as well. (Delivered in the earlier paintscheme)
RMAX 100-124 PC&F 1956 52'6"
RMAX 125-174 PC&F 1958 52'6"
RMAX 175-324 PC&F 1960 53'2"
There was also a series of 10 mechanical meat reefers that are close to the MTL prototype
RMBX 9000-9009 PC&F 1962 56'10"
Renumbered to RMAX 80-89 by January of 1972.
Hope this is helpful, obviously consult pictures to match paintschemes to numbers since ART liked variety it seems!