There's no need to open the rear.
After removing the tire, remove brake caliper and properly support it to prevent damaging the brakeline (no need to disconnect the brakeline).
Disconnect the parking brake cable at the diff.
Remove four nuts securing the brake backing plate to the axle tube.
Pull axle straight out.
The special locking collars are available at your favorite Alfa parts vendor.
Please see
this thread for a bit more info.