[bobcowan]

You don't want it rolling around in there. It will damage the radiator from the inside, and probably eventually put a hole In it. Plus, it could theoretically get sucked up in to the water pump, and then more bad things will happen.

The drain bolt is usually a tapered plug. If you pushed it through the tapered hole, now the hole is larger than it used to be. It probably won't seal on the new plug. As said above, you'll need drill and tap to the next sized hole.

Be sure and inspect the area around the drain port very carefully. Pushing that plug through may have cracked the boss. If you're not careful, you can also crack it when tapping new threads.

You're probably going to find that it's faster and easier to just pull the radiator out of the car.