The enlightened Jesuit Andrés Marcos Burriel, who since 1750 had been in charge of searching the archives of Toledo Cathedral and editing manuscript sources to learn about the history of Spain, planned to make a collection of all Spanish law, which was to begin with the edition of the Fuero Juzgo. Manuscript BNE 683 contains this unpublished edition, dated 1755, which presents a main text, that of the Murcia ms., and an apparatus of notes with the variants of other Latin and Romance codices kept in Toledo. The Romance codex designated as Toledo 4 represents for Burriel a version of the Fuero Juzgo corrected by Alfonso X with respect to the Murcian version, which he considers to be Fernandine. This study analyses how Burriel put together manuscript BNE 683 and explores the use that the RAE made of it in the edition it published 60 years later. In addition, Burriel's hypothesis that T4 transmits a translation of the Visigothic law corrected by Alfonso X is put forward, some of the particular features of T4 that we have recognised in previous research as being of Alphonsine inspiration are summarised, and Book 8 is analysed for further indications of Alphonsine influence in T4.