The flat plate that is in front of the bell housing toward the exhaust pipe is called the inspection plate. You can put 3 bolts in there if you want. It isn't structurally needed.
The oil that you see could be the rear main seal, but it also could be the back side of the valve cover leaking as well. 2 very common leak spots for a Jeep YJ motor. Both end up in the same spot so to decipher you need to look up at the back of the block, if its dry replace the rear main.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...