It's good to see an article which shows the opposition of many bishops at the council toward ƈσmmυɳιsm, and that they signed the petition which stated that ƈσmmυɳιsm should be condemned at the council. The docuмent was signed by 450 bishops.
The article mentions the study group which was called 'Coetus Internationalis Patrum,' and this was the group which put together the petition. The article says that Archbishop Lefebvre was a part of the group, but it doesn't make mention of the fact that Archbishop Lefebvre also founded the group, with help from Bp. Sigaud and Bp. Antonio Castro de Mayer, and it was Bp. Castro de Mayer who presented the petition to the council.
Here's a little more info from an article originally posted by the Angelus Press in 1991, which is a biography of Bp. Castro de Mayer after his death in 1991. He died four weeks after Archbishop Lefebvre died.
Bishop Antonio de Castro Mayer - District of the USA (sspx.org)