The structure of which you have spoken is quite good and simple, this tree should reflect it
pom.xml (aggregator, packagin pom)
- EAR-front-end
- WAR-business
- JAR-integration
So let's start from creating your own empty structure, then starting with integration of the various parts of the old structure, beginning from the integration layer...in turn integrates also a solid structure of unit tests, I would not exclude the possibility of dividing even the three main entities, the EAR , the WAR and JAR (integration) in sub-modules to increase the modularity of the application and facilitate the integration and maintenance activities.
I hope this can be a good starting point