The cache is not at the above coordinates; they will take you to the triangulation point at Three Barrows.
Stage 1: Use your OL28 1:25000 map
At the Three Barrows triangulation point, you head downhill in a westerly direction until you meet the dismantled railway. You follow the dismantled railway until it bears off approximately ENE direction at which point you leave the track and head downhill in a westerly direction until you meet a river. You follow the river north up to the point where an ancient stone row crosses the river. Which OS grid square are you now in? Grid = ABCD
Stage 2: Visit the trig point and obtain the four digit number from the base plate. Trig No = EFGH
The cache can be found at:
N 50 (D-B) A . (F+H) G (B+G)
W 003 (E+G) (D-E) . (A+E-F) G (G-F+B)
Please DO NOT post information of the brass plate in your logs or photos.