What the Archbishop taught and believed is different than what you will here now from the various priests in the SSPX. This claim come from on of his books:
Archbishop Marcel Lefebvre, Against the Heresies, p. 216: "Evidently, certain distinctions must be made. Souls can be saved in a religion other than the Catholic religion (Protestantism, Islam, Buddhism, etc.), but not by this religion. There may be souls who, not knowing Our Lord, have by the grace of the good Lord, good interior dispositions, who submit to God... But some of these persons make an act of love which implicitly is equivalent to baptism of desire. It is uniquely by this means that they are able to be saved."