Turning Towards the Lord - Orientation in Liturgical Prayer by UM Lang
Read the introductory chapter of this profound book, studying the history and question of the positioning at the priest at the altar.
Lang doesn't call for a return to ad orientem necessarily in its entirety, but at least for those parts of the liturgy directed to God -- particularly the Eucharistic Prayer.
Also: read the Foreword to this book by Cardinal Ratzinger / Pope Benedict XVI
Foreword to U.M. Lang's _Turning Towards the Lord: Orientation in Liturgical Prayer_
By Joseph Cardinal Ratzinger