Look thru the differential - along the axle holes. Are there "buttons" between the side gears? The "button" is a sort of large and thick washer with a threaded hole in the center.
If the diff is from an older car the rear inner joints in the axles are "female" and then there are (similar to the front) stub shafts which are attached to the diff with long bolts rather than C-clips like in the front.
I have one of these and checked - no grooves for C-clips in the side gears.... see photo - also the button is visible. The other attached photo shows the stub shaft and the mounting bolt.
I hope I made some sense....
Tapani
PS the 4.11 geared ACT tranny is from a 2.2 N/A Legacy..... it has fewer plates in the clutches and a higher stall converter - not really ideal for the SVX, but probably okay with a sensible right foot....