The dumbsheets forgot to drill the timing cover when they installed the aftermarket
oil pan. I doubt there is a plug, you will have to remove the timing cover and drill a hole or get a pan with a plug. You will have a very difficult time finding the "flat" on the timing cover if you do not know where it is. I went to a junk yard and finally found one. You could order a new timing cover with the plug, most will also have the fuel pump boss which you will have to use a cover plate.