Greg Robertson (aka 3-48s) gave a quick overview of governors when answering a question on the CJ2a Page forum. It is the best summary we have seen.
1)King Seeley was the first one * 1945-46 (some were dealer installed post production on later years). Most sought after & rarest.
2)Monarch was the second one * late 1946-48 (some were dealer installed post production on earlier and later years). IMHO This the prettiest with aluminum housing and bright tags that have a nice contrast to the black mounting bracket.
3)NOVI was the third one * 1948 – 50s (some were dealer installed post production earlier and later years) There were 2 versions of the NOVI for CJs and 2 versions for Empire tractors. The early NOVIs had an aluminum (Congress Drive) pulley with the later ones having a cast iron pulley. The Empire had the same, however the Empire long arm had an inboard offset to the arm.
This is an early NOVI w/aluminum pulley for my 48 CJ2A
In addition there were numerous Governors for stationary units such as Welders, Generators, Compressors, ETC. These other governors were not used on CJs.