Ya know gents there is a goodly bit of info out there on guns a like this.
In the early 60's a gent by the name of Robert D Fritz advertised in Model Railroader Magazine for railway gun plans and photos. Out of curiosity I sent off for his catalog . It was full of plan sets and photos so I sent off for one. I received a very well drawn set of plans with multiple views, sectionals, cutaways as so on. I still have them somewhere (I've been kicking myself in the fanny ever since for not going back and ordering more). Plans were available in HO scale to 1/2 inch to the foot scale. Prices were dirt cheap (which was great because I mowed lawns back then at $2 each, lol).
He lived in Lutherville, Maryland which I believe is right next door to the Aberdeen Proving Grounds where guns like this were developed and tested. There was a museum on base (which may still exist) about railway guns and he was associated with it in some way. He has long since passed away but his plan and photo collection may still exist at the museum.
Most guns like this were for WW1 abut a few existed for WW2. All were incredibly big and heavy. Some have been preserved (the German Leopold for example). Almost all had multiple bogeys with 4 to 10 wheels each. One had two bogeys with 16 wheels. Considering the wheelbase (around 30 ft) it must have had some sort of lateral motion devices built into the journals. Many used leaf springs like on steam loco drivers rather then coil springs due to the weight. Special routing was almost certainly a must due to weight and clearances. These were probably high priority consists as well (which must have driven dispatchers around the bend now and then, lol). A considerable number of support cars were required for ammo, powder, spare parts, tools, crew, and so on. Would definitely make an interesting consist on a route.
Firing was not fast. 5 to perhaps 30 minutes per round depending on the size (bore) of the gun. Some required a hole in the ground to accommodate the recoil of the barrel. Maximum elevation was limited to around 45 degrees. No side to side motion was possible within the gun itself. Instead they were located on a curved section of track for lateral aiming. Recoil was considerable. Many had winch assemblies on the front to haul them back into firing position.
Info and photos can be found on the web. Search for Robert D Fritz, Robert D Fritz railway guns, railway guns, and so on.
Ben