For chain suspended good mornings, you set youself up under the bar, then lift it from the bottom position.This is similar to doing a bottom-position good morning from the pins inside a power rack, but with the bar suspended from free moving chains, it is much easier to get the bar into the correct position on your back.When performing a good morning off the pins in a rack, your set up position must be exact or you will sacrifice alot of energy fighting to get the bar off the pins.It feels very awkward if you are not in the correct position.
In regards to the 36 inches, I think that is in reference to the lifters height.From what I understand, most lifters set the height of the bar about even with their navels.For some this could be 36inches or 39inches,etc.