Welcome to Elliston! You will miss some of the magnificent coastline if you stick to the Flinders Highway, so pull into town, get the numbers to find the cache, and enjoy the scenery.
At the listed coordinates you are in front of Elliston Post Office.
Let ABCD be the number of the PO Box below #1580
Let WXYZ be the number of the PO Box below #61
The cache is located at S 33º 39.(A + W)(B - Y)(B - D) E 134º 53.(X - W)(Z - D)(B + Y) Checksum of decimal fractions 22
It's an easy walk from the listed coordinates to GZ, you can drive if you prefer, but once you've found the cache, please take the time to cross the road and take in the scenery. There are numerous "cloggs" in this area, referred to in caches GC9CEQA and GC51TTM. Have fun!