If the rime of the old freeze plug is intact and not rotted away, a smaller freeze plug can be installed inside the rim of the original plug. This can be either a drive-in plug or an expansive (rubber) plug, but will need to be sized to fit the I.D. of the original plug and not the hole in the block. Your parts store should have the original plug available so that you can use that to size the "piggyback" plug instead of having to stand on your head and fold yourself in half to get in and measure the existing plug.