I have had similar problems with split/cracked union nuts on pumps. Because parts supply in the UK is particullarly poor I managed to fabricate something very similar to what you have there. My method is much more 'ghetto' but it works perfectlly well. Simply remove the broken nut, place the split nut around the union fitting, screw it together and screw the union back down onto the pump after fitting a new seal if required.
It's a simple way of repairing what can be an awkward problem especially if you have to replace several fittings in order to be able to glue a new union into place. It saves the customer some money and keeps them happy.
For anyone else making this type of repair, don't use PTFE tape, silicone or solvent cement on the broken union nut as in my opinion it's just a temporary bodge that will eventually fail again.