Hart Park may have had more than one roller coaster over the years. In a historical story about Hart Park a quote from Gus Jr. of the Balasis family (Gus and Pearl Balasis) operated various concessions said the following:
"About 1940 my uncle brought a merry-go-round from the East and put it together piece by piece. After that my father hired a company to design a wooden roller coaster, and he put in the Ferris wheel. Later he put in a much bigger, metal roller coaster. After that came the kiddy rides, the little train, a tilt-a-wheel, and the electric bumper cars."
The 1959 date of the Comet Jr. comes from Richard Munch's 1991 Roller Coaster Directory. Assuming this is accurate the Comet Jr. would probably have been the second roller coaster based on the dates. Gus Jr. said this was a steel roller coaster which could be explained by the NAD coasters of that time using steel structures. What isn't so easy to explain is the mention that this was a "much bigger" coaster when a Comet Jr. is already a very small roller coaster -- even at that time.