I hope I don't get accused of trying to reinvent the wheel here. There is already a perfectly good traditional cache highlighting this post office (GC24PZY "Daveyston's Old Post" by DJC 3575 placed in 2010 which I encourage you to find) and I've already covered postcode 5355 at Stockwell. However, this is a pretty special post office, worth another visit. Plus I thought it would be nice to have a quick and fairly easy letterbox for you to find as you head towards Nuriootpa and beyond on the Sturt Highway, or alternatively, on your way home.
At the listed coordinates, you are at an intersection. I've tried to separate the icon from that of the existing traditional. Can you spot the post office from here? Use the abovementioned traditional's coordinates if you are having trouble.
The structure is adjacent to what was a general store which acted as an unofficial post office. When the store closed, mail continued to be delivered to this shed until relatively recently. The sign on the structure states that it was in service from A - B - CDEF to GH - J - KLMN.
The cache can be found at S 34º 28.(A + H)(E - J)(M - K) E 138º 52.B(H + N)G. Checksum 27 for the decimals.
The cache is less than 250m away. The terrain rating is based on the direct route in as at May. It will get harder after heavy rain, or you can make it easier by going the long way around, but DO NOT attempt this as a park-and-find from the new highway.
Please leave the stamp in the cache, and the replace appropriately. Thank you, and have fun.