You won’t like it, but my best advice is to take the engine out.
Even if you manage to get the sump off and past the rear cross member housing the torsion bars, the long side gaskets are designed to be trapped under the main bearing caps and the bearing cap seals needs to be offered up and cut to length in situ.
In my experience, the job can only be done properly with the engine out and upside-down. Sorry.
B……
Bernie