אֵין בֵּין סְפָרִים לִתְפִלִּין וּמְזוּזוֹת אֶלָּא שֶׁהַסְּפָרִים נִכְתָּבִין בְּכָל לָשׁוֹן... רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר, אַף בַּסְּפָרִים לֹא הִתִּירוּ שֶׁיִּכָּתְבוּ אֶלָּא יְוָנִית:
There is no difference between BOOKS [of the Tanakh] and tefillin and mezuzahs except that BOOKS may be written in any language ... Rabban Shimon ben Gamaliel says that scrolls [of the Tanakh] were permitted to be written only in Greek.
How is a Kosher Torah scroll written in Greek - is there an accepted unified Nosach or does anyone translate as he sees fit? Does one use the Greek Alphabet or Ashurit? Do all the rules of writing a Hebrew-language Sefer Torah (Rambam ibid 7) apply to it also (lines, spacing, big and small letters, omitted and extra letters?
I don't ask if there's masora as in the related question. Since the Mishna states it is possible I'd like to know how possible it WAS done.