The cache is NOT at the posted coordinates, but you need to start there. Within a few feet you will find a square stone with a picture of an acorn. The final can be found at:
N 41° 48.ABC W 088° 10.DEF
A= # of times the letter "R" appears in the plaque.
B= 4th digit of the smaller year.
C= 1st digit of the larger year.
D= Number of non-numeral words.
"1FE Years"
As always, watch out for muggles at the final.