In response to my question about the reference to some sort of BCL guidelines on the celebration of the 1962 Missale Romanum ("It will implement the guidelines to be offered by the Bishops' Liturgy Committee." -- see Letter of the Bishop of Norwich) a reader kindly sent me some information on this.
Apparently the matter relates to a series of questions that came to the American "BCL" (Bishops Committee on the Liturgy -- since renamed the "Bishops Committee on Divine Worship) from brother American Bishops. This resulted in the forumlation of 40 questions and answers that were sent to the American bishops, with other questions that remained being sent on to Rome as dubia.
These dubia involved:
a) the question of "stabiliter" or "continenter" and how that is to be understood and applied
b) the question of how the new code of canon law does or does not impact the ancient liturgy (e.g. specifically mentioned are matters like the celebration of Mass in the afternoon, the use of female altar servers, concelebration, the length of the Eucharistic fast)
c) the question of whether priests may act as deacons or subdeacons as they used to and whether a deacon or instituted acolyte may act as a subdeacon
d) the issue of the vernacular readings and what this intends to mean or not to mean as regards the new lectionary, and otherwise from which English language source they should come from
e) finally, what form of confirmation should be used
These 40 Questions and Answers and the 5 dubia can be found here:
Forty Questions on the Apostolic Letter Summorum Pontificum.
Evidently the "BCL guidelines" referred to would be made up once a Roman response to these matters is received.
Of course, the apparently imminent forthcoming document from the Ecclesia Dei Commission sounds as though it is intended to answer such questions in a definitive way. One hopes, even expects, that it will become "the guidelines".