For a 3.42 gear you need an orange governor rear and a 30 tooth blue.
The orange gears are hard to find.
You can also use a green governor gear out of a MonteSS and a 27 tooth black gear.
HTH...Brian
Brian, does the orange gear have 11 teeth? If so, according to my 1986 MAKE:B "G" CAR Speedo Gear Usage Chart, the code is "E" and the GM part number is 8634965.