There should be two posts on the BOTTOM that the radiator use for mounts, they drop into openings in the rail underneath. The left one (drives side in W123) should have a plug and I have seen blue plastic screws also, be prepared to let it hang if the barbs on it are still there, they are supposed to retain the drain plug but can break off.
Unless you have a stubby driver handy just reach in your pocket for a quarter - been my preference for a long time!
DDH