Callistemon are great for bonsai.
This Callistemon is quite tall and thin. Maybe you will consider pruning the trunks a little more at some stage. Also consider leaving some deadwood. callistemon wood is soft and rots reasonably quick unless you treat regularly but dead wood is a regular part of many Aussie trees due to the harsh conditions down here so we are seeing more dead wood on our native plants now as Australian growers become more confident of Australian inspired styling.
Great job on the smaller trunk reduction. You should see masses of new shoots erupt over summer now. Get some treatment on that dead wood soon so it does not rot off too quick. Long jin matches the other trunk for now but maybe you'll be brave enough to reduce the main trunk sometime??????