This in an easy puzzle, and requires you to only find one headstone. All the information you'll need can be found at that one spot.
The final can be found using the following information:
N 41 A.BCD W 74 E.FGH
A- The day Sallie Lane died
BC- The last two digits of Sara Marsh's birth year
D- The last digit of Sarah Marsh's death year
E- The month Martha Wood was born
FG- Last two digits of Joseph Wood's birth year
H- Last digit of the year Sallie Lane died