OK so it looks like there are (at least) two similar versions out there. There's
this one which is published by George Routledge & Sons, 1878. It doesn't give the translator, but the text is similar to the PG one.
The later looks like an update/revision of the former.
For example the preface in the Routledge one refers to "Bibliothèque Royal" whereas the PG refers to "the Royal Library". Or in chapter one, we have "the bourg of Meung" v "the market-town of Meung". Otherwise those respective sentences are the same. And there were other examples.
Wikisource has a copy from the PG text, and their
talk page about it claims it is the "1894 Robson translation" based on various links only some of which still work.
This appears to be the same text but is dated 1893.
So I'm pretty convinced that these two versions are related, and one is claimed to be a Robson translation. So for the purposes of my Calibre library and to distinguish it from the Pevear 2006 I'm going to label it as Robson.