If your looking for an HF transmission, it would be a good idea to give some additional information. 84-87 was one design. 88-91 is a completely different design. 88 is not 100% compatible with 89-91, but it's primary difference is the spline count on the main shaft is different, so you have to use a clutch and pressure plate for an 88.
Then their is the question of if you are looking for a CA version, Fed version, or High Altitude version. The CA version isn't geared quite as long as the Fed version, although it's still geared longer than a DX. I'm not quite sure what the difference is on between a Fed version and the High Altitude version.