Though you don't mention it, I assume you've removed the rear spring.

Unless you're willing to cut big holes in the floor to reach those bolts
from inside the car (not recommended), the rear crossmember has to come
out. It is held in by one bolt at each end of the crossmember that goes
up through a large round rubber bushing that fits in a sombrero-shaped
stamping on the frame. The bushing tends to get "welded" into position
over time, so it may take quite a bit of persuading. Leave the outer
cover bolts in place hand-tight. Find a long crowbar and pry between the
crossmember and the frame (strategically-placed pieces of wood might
minimize cross member damage). Put something close beneath the
differential to catch it so it doesn't crash to the concrete.