The given coordinates are for Cowley church. Look around outside for a dedication to D. C. Workman, born 19AB, died 200C. Now convert from A to DG, from B to EH and from 9-C to FI, by the rule:
0 -> 48 5 -> 23
1 -> 91 6 -> 89
2 -> 75 7 -> 04
3 -> 17 8 -> 32
4 -> 66 9 -> 50
(( For those whose GPSr doesn't like the table above, the rule is to change: 0 to 48; 1 to 91; 2 to 75; 3 to 17; 4 to 66; 5 to 23; 6 to 89; 7 to 04; 8 to 32; 9 to 50 ))
The main cache can then be found a couple of minutes' walk away at N 51° 49.DEF W 002° 03.GHI . If you're stuck and would like to see a spoiler photo from Google Streetview then click here.
Cowley Village is one of eight caches around Cowley County Parish ... why not get out there and see them all! I recommend tackling the circuit anticlockwise, starting/finishing here.