This collection of caches has nothing to do with the Church Micro series in the UK. Given that the Australian 2016 census indicates that No Religion and Jedi Knight are the fastest increasing classifications of the optional religion question "What is the person's religion?" it is not surprising that there is surfeit of empty churches that have been repurposed.
Some history
The former Terowie Baptist Church building is now privately owned. It was built about 1880. No other details are known.
Now to find GZ
If the church has brown doors then use S33 09.312 E138 54.988
If the church has green doors then use S33 09.386 E138 54.932
If the church has blue doors then use S33 09.483 E138 54.877
good hunting!