At the posted coords look at the building to the east for a 4 digit number. (just right of stairs) Let these 4 digits = ABCD
At waypoint 2, go towards the entrance of the theater. Look to your left for some black and white photos of historic St Helens. There will be 4 on left and 4 on right, once you are facing the photos. Using just those on the left side, the 3rd one down has a 4 digit number on it. Let those 4 digits = EFGH. The photo just below that one has a 2 digit number on it. Let those 2 digits = I and J.
Now for some simple math to find the final coords.
Final = N45 51.(B-I) (A-J) H W122 47.(F-E) (B-H) (D-E)
Cache has been moved slightly in hopes it might stay put. Math has been adjusted and a new hint added.