If your Xj is unlifted, you need to partially detach the front axle to let it droop. When I did my 87 it took a lot of drooping and was still a tight fit, requiring the removal of the oil pump pickup.
Before you go too far in this, I suggest you give it a good look, because it's really much more likely that the leak is from the oil filter adapter, which tends to look like a gasket or rear main leak, or perhaps even from the rear of the valve cover gasket. It is also possible for the rear bolts of the oil pan to loosen, and before replacing the gasket you should make sure the bolts are all properly torqued.