With regard to the question of Holydays of Obligation, you state that your understanding is that "the Holydays of Obligation established by the Bishops' Conference of England and Wales and confirmed by the Apostolic See under Canon 1246 are to be observed by the whole Church in England and Wales in celebrations of both the Ordinary and the Extraordinary form of Mass." I understand that in England and Wales the Feasts of the Epiphany of the Lord, the Ascension of the Lord and the Body and Blood of the Lord have been transferred to the nearest Sunday with the approval of the Holy See. Since these Holydays are to be observed by all of the faithful, priests who celebrate according to the 1962 Roman Missal for the benefit of the faithful "attached to the Latin liturgical tradition" should also celebrate these Holydays on the prescribed Sundays.
This text wasn't quoted, only indirectly referenced, on the website of the liturgy office of the English bishops.