Think of it in terms of BMI (body mass index).
Most top runners have a BMI of around 19.5 to 20.2
The average BMI of all the qualifier for the US Olympic Marathon Trials is about 20.0 The elites of that group (sub 2:15) are just under 20.0 on average and the 2:16-2:22 guys are averaging just over 20.0.
For someone who's height 6'2" (74 inches) your weight would have to be at 156 lbs to have a BMI of 20.0
It's hard (if not impossible) for people with medium to large bone structures to reach this type of BMI number. Most elite marathoners have small bone structures.
Try this simple test:
Wrap your fingers around the wrist bone of your other arm. If your thumb and middle finger can touch but don't overlap you likely have a medium bone structure, if they can't touch you likely have a larger bone structure and if they overlap then you likely have a medium bone structure.
If you are of a medium bone structure I would suggest targeting about a BMI of 21.0 (163 lbs) but if you have a small bone structure try and get down closer to the 20.0 range and 156 lbs.
Thats my 2 cents worth.