If Moser has specs for 9C1 (narrow) and WX3/Impala (wide), it should be easy enough to tell them what you need.
The
Moser Impala SS axle shaft is listed at 30.938".
The calculated difference in track width of the Impala vs wagons can be calculated as follows:
Impala - 1598mm flange to flange (axle shaft to axle shaft)
wagon - 1642.5mm flange to flange
Difference = 44.5mm, divide by 2 (for a single shaft length difference) = 22.25
Divide 22.25 by 25.4 = 0.875" (7/8") longer than the SS axle shaft
Tell Moser you need shafts that are 31.8125" long. Also, the shaft wheel bearing journal diameter is larger at 1.600" compared to sedan axles.