HI, I will just add my two pennies worth, having just completed this job.
The way I tackled it was to remove both rear outer wings and the fuel tank. Once I had removed all traces of the old Xmember I fed the new Xmember through the rh rear wheel arch into the area where the fuel tank sits, I then proceeded to pull it into position at the same time rotating it so the hinge brackets would pass under the floor. This operation took under a minute to perform. The only difficult part is to fit the body rubber mounts. I used a 6’ x2.5’ dia crow bar to lift the Xmember into position. Once I had the rubbers fitted the Xmember found its correct position so all the height measurements I had taken prior to strip down were ignored. As I do not weld I bolted the Xmember to the body and pop riveted the boot floor to the Xmember.
The only problem I had was removing the fuel tank, this led to the fuel pump and fuel lines having to be replaced.
All the above was achieved without anybody helping me, so I would sum up the job as being very very easy.