Matthew, since you are on the other side of the planet you should have taken the back off first, oh well too late now.
Fine looking bass there! Good luck with her.
To carve the back brace out it shouldn't be to difficult. You might be able to get some controlled splitting and remove the big chunks first, then once down to a bit thinner, you can plane it or keep using a sharp thin headed gouge, finger planes and then wet the last slivers with a damp cloth to remove the splinters and clean the glue off.