I have Briley tubes in two of my shotguns, a Browning Double Automatic and a Winchester Model 12. You cannot see the tubes unless you look directly into the barrel. A$786 sounds pretty pricy, especially since Briley installs them in a double barrelled gun here for US$399, including five choke tubes.

I have just e-mailed Briley to find out if they have an authorized representative in OZ who can perform the work for you there and will let you know what the response is.