GM Turbo Hydro 400 Fairbanks Superior Transmission Posi Shift 2 Stage Kit 1965-Up This 2 Stage Shift Kit from Superior comes with two levels of performance: 1. Heavy Duty 2. Street & Strip This shift kit firms up 1-2 and 2-3 shifts, will work with 6 or 7 check ball cases, replaces worn out separator plate with the new special design plate, and improves overall performance. The Posi Shift 2 Stage Pac's are by far the easiest available way to step up transmission performance and can be installed with the transmission in or out of the vehicle.