Kaiser-Frazer began to get Hydra-Matics from General Motors in June 1950. By that point, the 4-door sedan production was ending, Vagabond production was wrapping up, and the daily dribble of Manhattan Hardtop and Convertible models began at the Jackson hand-craft line. While overdrive was an option on the standard models (4-door sedan and Vagabond) according to K-F factory production data, they were equipped with o/d except by special dealer order (manditory option). Once the automatics started to come in, they were installed on the Manhattans for the rest of the run. Convertible production finished prior to October 31, 1950 and the last Manhattan hardtops were built in November 1950.
The production run reflected built up bodies or major assemblies and stocks of body panels that had more value on a finished vehicle than as scrap. As far as information goes, no built up 1949-50 cars were turned into 1951 Frazers, other than perhaps a few for prototyping as they would make excellent references for the sheet metal tooling. Kinda like the 1955 Hudson program using a couple prototype 1955 Nash cars to verify mating parts.