What makes these different from the regular large key 1970 - early 1971
syncro gear assembly(# 3410305 & 3410300)? They all use the same improved stop rings. Thanks.

NP changed the shifter side cover and shifting forks in 1971, not sure of exactly when Those changes did help those trannys shift easier, maybe they changed the sliders also to get along with the steel forks I've had all three generations of the NP833 as well as the overdrive versions apart, the 1971 and later synchros are the cats meow