I have one drawing from a military instruction of 1918 of how the gun must be setup in position, and a picture of the gun in position but on wooden platform and without cingoli.
Let me know if that can help.
All the very best
__________________
Eric
On going : Obice da 305/17 su affusto de Stefano, Mark 1 female ...
Finished : Dennis 3 tons lorry, Jeffery Poplavko, Renault EG, Renault FT
Histoire de Guerre (GBM) number 82 (avril-mai 2008) has six pages on this artillery piece by m.Vauvillier. There are photographs of this modification and a commentary which states that it was officially adopted in the autumn of 1914. For your purposes, the photographs and a 1/72 scale drawing included in this article would seem to provide the information that you want. Back issues are still available. (I was intending to build this model too, but it is in the collection for attention later...)
The "cingoli" were adopted for 120L by the "Projet provisoire" dated August 9th 1913. The use for the 120L and the 155L was ordered by the "Instruction provisoire sur l'emploi des ceintures de roues et de leurs accessoires" dated Juni 12th 1914. The"cingoli" for the 155L had 12 "plateaux" and 12 "segments", the 155L model 1877 with "cingoli" had the following wheels "roues n° 1 bis". Nota: the 120L Mle 1878 with "cingoli" had wheels "roues n°9", the "cingoli" had 10 "plateaux" and 10 "segments". Yours sincerely, Guy François.