The downside to the early first generation NP833 with the OEM synchors was hard shifting, cold weather or not. ATF help alleviate the hard shifting problems The third generation synchors, 1971 and later versions, help a bunch also I have replaced the early syncho asemblys with the later version along with the steel shifting forks for several customers You can to There are three differrent versions of the NP stock synchro assemblys I've seen, 1964 to 1966, 1967 to 1970 and 1971 and later Two different side covers and two different versions of shifting forks also in those