These models were made by F. & F. Mold and Dieworks in Dayton, Ohio. They were included in specially marked Post cereals. F. & F. was well known in the late 1950's and early 1960's for their plastic promotional giveaways. Many food companies such as Aunt Jemima and Post used their services.
F. & F. also made models of the 1955 Thunderbird and 1964 Mustang, among others, as prizes in Post Cereals.
These models are about 3 inches long.
A pair of Hard Top 1959 Thunderbirds. Note it is difficult to find these models with complete front vent windows. In the manufacturing process often the vent windows were only partially formed and have gaps.
Photo courtesy of Gary Kerr.
A pair of 1959 convertibles. These models were available in many colors.
Photos courtesy of Zargon Quadratvogel.