If anyone would like to try to design a WW1 French railway gun the manual for the gun with drawings is on line at:
Reglement de manoeuvre de l'artillerie. Titre V7, Description et entretien des materiels sur affut-truc a* glissement a* deux bogies et de leurs munitions / Ministiere de la guerre | Gallica.
This gun was a Schneider a glissement (sliding) mount. This used a system of wooden blocks jacked down onto auxiliary rails to absorb the recoil.
Regards,
Charlie