Are there 'Magisterial' explanations of why we should face East to celebrate the Most August Sacrifice of the Mass? I would like to know if there are. Curiously, the only such one that I know is ... YES! ... in the Post-Conciliar Liturgia Horarum!! Turn (if you possess a copy) to the Monday after Lent 4, id est next Monday. You will find Origen's passage on Christ our Propitiation, with its quotation of Leviticus 16:14 'and he shall take of the blood of the bullock, and sprinkle it with his finger upon the mercy seat eastwards', and Origen's comment 'the fact that he sprinkles eastwards is not something you should take lazily; it is from the East that Propitiation comes. For it is from there that the Man comes whose name is East (anatole), who is made mediator between God and Man'.
Back in my Anglican days, as I celebrated Cranmer's Liturgy in deepest Devon, I explained to the congregation that, having concluded the 'Comfies' with S John's phrase '... for He is the propitiation for our sins', I would turn to the East whence comes our propitiation and sprinkle the Blood of the New Covenant over the Heavenly Mercy Seat which in the Holy Sacrifice of the Mass is made one with the Altar of our earthly church building. Perhaps I should fish that homily out for use again, now that we have the Ordinariate Use of the Mass, with the 'Comfies' optionally available.
But if the wonderful people of Broadwood Widger (yes! English villages really do have names like that!) had picked up the Neo-Vulgate, they would have found that the word 'eastward' no longer appeared in the text of Leviticus - the translation I have given above is from the King James Version. You see, after the new breviary was authorised (1971), the new edition of the Vulgate appeared (1979), with 'eastward' omitted. Subsequent editions of the Liturgy of the Hours brought its biblical lections into line with the Neovulgate. So the Patristic Reading for that Lenten Monday, chosen to be a commentary on the Biblical Reading for the same day (Leviticus 16:2-28), now explicates a text different from the one which has just been read, with the crucial words missed out! Such is the wonderful world of endless liturgical Improvement by Experts!
Incidentally, modern translations go back to 'Eastward'! Such are the whimsical vagaries of "scholarship". In any case, I wonder if enough thought was given when the Neo-Vulgate was devised to the fact that it would create a hiatus between the Bible in people's hands and the Bible upon which the Fathers and the Schoolmen wrote their commentaries (a loss, one might say, in diachronic unities).
The Neo-Vulgate revisers evidently thought that basing their translation upon the consensus of modern ecumenical scholarship (for example, the Neovulgate New Testament is essentially based on the Aland/Martini text 'qui nostris temporibus, communi consensione, summam habet auctoritatem') would be good ecumenically (reinforcing, as it were, some synchronic unities). But it needs to be pointed out that the old Vulgate is very often in agreement with the Greek Septuagint, which is still the base text used by the Orthodox.