Another approach: The Sun
Assuming Sun rays are parallel all over the globe, lets see how high the Sun is above the horizon (local horizontal plane) --> the elevation value at timeanddate.com
seen at the start and end point.
I found
Shark Bayand
Sunshine CoastI take Dec/22/2018 - solstice day, as the Sun's path is nearest to these two points.
I take Shark Bay local time 08:55h, as Sun's azimuth then is 99°, which fits with the Great Circle course to Sunshine Coast.
99° would be the direction you have to look, to see (theoretical, it's much to far) Sunshine Coast from Shark Bay.
Sunshine Coast local time is then 10:55h according time zones.
Sun Data at Dec/22/2018 08:55h Shark Bay local Time:
Shark Bay (08:55h): Azi. 99° Elevation 43°
Sunshine Coast (10:55h): Azi. 78° Elevation 78°
The difference in elevation of the Sun at the same time is 35°
That's what the local horizontal planes at Shark Bay and Sunshine Coast are tilted against each other.
So starting at Shark Bay you would have to curve down for 35° on your way to Sunshine Coast, which also is the result in RonJ's calculations.