Yes, the SVX is the only Subaru I have run across that uses 2 different rear axles, one having a longer input spline on it, so to use those other Subaru Rear diffs, you will also have to deal with the change in axles (not sure if the their axles would fit up to the SVX spindles, but maybe)
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Huck
Subaru Ambassador
92 SVX LS-Tour Magnaflow Exhaust, 5-Spd-AWD
88 XT6 AWD 5-Speed "Bride of FrankenWedge"
15 Impreza Premium Sedan
15 Crosstrek XV 5-Speed
My 5-Speed "How-To" Write-up
1976 Pontiac Firebird Formula
Current Count of Subaru's Owned.... "70"