What a beautiful old tree! I am not sure you can repair this damage. You will need to cut the large branch at the trunk where it has split. The tree may heal the wound over in time. However, the shape of the tree is probably ruined. You could cut the entire tree about a foot up and then graft some new cultivars on next spring but that is a lot of work. Cut the broken limb off when it is dry. No wound paint is necessary.

Ann Hazelrigg
Plant Diagnostic Clinic