Since the Orthodox Church has the same seven valid sacraments as the Catholic Church, the only requirement for a baptized Russian Orthodox to enter into full communion with Rome would be to make an abjuration or a profession of faith.
Reception of Converts and Profession of Faith
According to the form approved by the Sacred Congregation of the Holy Office, July 20, 1859.
In the case of a convert, careful inquiry should first of all be made concerning the validity of their former Baptism. If it be found that there is no Baptism or that the Baptism received was invaid, they must now be baptized unconditionally. If, however, after diligent inquiry reasonable doubt remains concerning the validity of their former Baptism, they are now to be baptized conditionally. If, thirdly, the former Baptism be judged to have been valid, only Abjuration or Profession of Faith should be required. In accordance, therefore, with their condition there are three methods of receiving converts:
I. If never baptized or if the previous Baptism was invalid -- The convert is unconditionally baptized, and neither Abjuration nor absolution follows, since the Sacrament of Regeneration washes away all.
II. If the previous Baptism was doubtful -- The convert is conditionally baptized, the following procedure being observed: 1. Abjuration or Profession of Faith and conditional absolution from censures. 2. Conditional Baptism. 3. Sacramental Confession with conditional absolution.
III. If the previous Baptism was valid -- 1. Abjuration or Profession of Faith. 2. Absolution from censures. 3. Supplying of Ceremonies of Baptism (see form for adults [or of children, according to more recent decrees]) if desired.
The priest vested in surplice and violet sits in front before the middle of the altar or, if the Blessed Sacrament is present, on the Epistle side. The convert kneels before him and with his right hand on the book of the Gospels (or the missal) reads the following: (If the convert cannot read the Priest reads it to him slowly and distinctly, so he may understand and repeat the words.)
**PROFESSION OF FAITH**
I, N.N., ______ years of age, born outside the Catholic Church, have held and believed errors contrary to her teaching. Now, enlightened by divine grace, I kneel before you, Reverend Father _____________, having before my eyes and touching with my hand the holy Gospels. And with firm faith I believe and profess each and all the articles contained in the Apostles' Creed, that is: I believe in God, the Father almighty, Creator of heaven and earth; and in Jesus Christ, His only Son, our Lord, Who was conceived by the Holy Ghost, born of the Virgin Mary, suffered under Pontius Pilate, was crucified, died, and was buried; He descended into hell, the third day He arose again from the dead; He ascended into heaven, and sitteth at the right hand of God, the Father almighty, from thence He shall come to judge the living and the dead. I believe in the Holy Ghost; the holy Catholic Church; the communion of saints; the forgiveness of sins; the resurrection of the body, and life everlasting. Amen.
I admit and embrace most firmly the apostolic and ecclesiastical traditions ...
For the remainder of the Profession of Faith on can read it here: Reception of Converts and Profession of Faith.
For those who wish to read it from the Roman Ritual (page 10) of the 1952 edition, but noting that the Reception of Converts is dated July 20, 1859. This should suffice for placing the Profession of Faith within the Jur Novissimum.
The canonical period known as the Ius Novissimum ran from the Council of Trent (1545-1563) to the promulgation of the Pio-Benedictine Code (1917).
Update
The original Rituale Romanum was promulgated by Pope Paul V on June 17, 1614 and has undergone several later editions, but has essentially remained the same.
Numerous new editions of the Ritual of 1614 were published, introducing changes of various sorts, generally enriching the part dedicated to blessings, and organizing the material better and with different titles. These were issued by Popes Benedict XIV in 1742, Bl. Pius IX in 1862), Leo XIII in 1884, Pius XI in 1925, and Pius XII in 1952.
Despite the various editions, the text which has come down to us remains essentially the same, and the use of it remains authorized and protected by the motu proprio Summorum Pontificum of July 7, 2007, as we celebrate the 400th anniversary of its promulgation. - The Fourth Centenary of the Rituale Romanum of Pope Paul V : June 17, 1614
