These transmissions can be used on the 83/85 bikes as a replacement for the 2nd gear problem. The gear ratios are wider spaced, giving a higher 5th gear. They can also be used in the earlier RSTD's that have a very high 5th gear that would make 5th gear more usable, especially with a V-Max gear, which is 10% lower geared. Are you confused yet?
The transmissions on the 85's, after serial number 1403 and up, have been pretty much bullet proof with the exception of the pins coming out on the front of the shifter tumbler. This was fixed on the 2nd gen transmissions with a cast part that did not have the pins. When a pin comes out, you can not shift above that gear.
RandyA