archiveBaseName = 'c-foo'
                }
                task barJar(type: Jar) {
                   archiveBaseName = 'c-bar'
                }
                task foo2Jar(type: Jar) {
                   archiveBaseName = 'c-foo2'
                }
                task bar2Jar(type: Jar) {
                   archiveBaseName = 'c-bar2'
                }

You can set each of these properties on the task separately.