Thanks, I know about it and it served as a basis on differentiation of Brittonic, for instance.Something you might find useful in the future: a "modern Gaulish" conlang.
Note, that said, that's based on late Gaulish and with a fair influence of Latin in cases and grammar. While I don't think Greek influence on Gaulish would be more important than IOTL (for exemple, -os genitive singular going from -ū)to -oi). Don't get me wrong, I'll probably use this website (I actually do partially) , which uses sources I have access to (see bibliography), but I think I' may have a different take on case simplification (the attested os>o, for exemple; giving something along epo rather than ép) and I'm unsure about a total disappearance of cases in the forseeable future.