This waterwheel-driven three-throw beam pump was installed in 1782 to pump water from the River Rother up to Petworth, 1½ miles away and 150ft. higher.
The given coordinates are for a suitable parking area, not the cache. You'll have to find an information board to answer these questions:
The railway from Pulborough to Petworth was built in ABCD.
and extended to Midhurst and Petersfield in EFGH
Now look around for the number on the Engine House = J=3 K=3 (can't be seen at the moment ).
Now the cache can be found at:
N 50 57.(D-A)(J+E)(H+K) W 000 37.(B-G)(G-E)(D-E-A)
You'll need to drive to the final location.
Onfr bs QC10.