Cadillac Repair: Drain Plug (petcock?) for 93 Cadillac Sedan DeVille, thumb screws, thumb screw

Question
QUESTION: We think the drain plug might have come out of my daughters 93 Cadillac Secan DeVille.  We think its also called a "petcock".  We want to know what it looks like and how easy/difficult it will be to put a new one in.

ANSWER: All it is is a plastic wing nut with threads on it. You can purchase one at most any auto parts store and it simply thumb screws in to the radiator .

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QUESTION: Our issue is that there seems to be some sort of "plate" under the car covering where we need to get into to replace the petcock. How do we get into/around that?  Where can I find a diagram online that will show these sorts of details?
And thank you!!!

Answer
I cannot find any picture location showing how to access the drain plug. I have always been able to turn the thumb screw by reaching down in between the radiator and the engine to the bottom of the radiator and unscrew the drain plug as the drain plug is on the inside of the radiator facing the engine.