jdfire,
The part of the moldboard plow that you are referring to is called the "plow share". It's the bottom part of the plow that has the rounded point on it. The "moldboard" is the large curved piece of metal that is attached/connected to and above the plow share. The plow share's rounded point lays on top of the "landslide". It lays on the ground and also sticks out behind the plow. Standing behind the plow, measure the distance from the landslide to the outside lower edge of the plow share.
This measurement will tell you what size moldboard plow you have. This is the width of a furrow the plow will make. Also, take half of the measured width of the plow, and that's the proper depth the plow should be used at. A 12" plow will make a 12" wide furrow at 6" deep. I would have taken a pic of my 10" plow, but my wife took the digital camera with her while trick or treating with the kids tonight. If you don't understand, I can take a pic later, and then post it. I hope this info will help answer your question.