Ok. The guys who have responded to your inquiries are more knowledgeable about this game than I am. However, I've been in your shoes and sometimes a few basics need to be broken down a bit for us new guys. I've been working on this game for a while now and I know how confusing this goofy game can be. Let's try a few simple steps for adding engines and cars to this game.
I had not looked at the Bigboy until this morning. I have a test map and I'm working on a new map - for a year plus now. Anyway, I downloaded the bigboy and the Santa Fe v3 passenger car for a little test. Here's how it went:
First, the game takes its direction from the xml files. As long as it finds the files you tell it you're using, all will be well. If not - CTD! I started my test by adding the SF passenger car. In my case I had a passenger car that I had repainted for my map.
Bigboy_traincar1.jpg
The passenger car kfm I've been working on is named LASL_Passenger_Car.kfm. There is a version 1 and a version 2 in existence. In order to test the SF v3 passenger car, I added the sf files that I downloaded this morning and just renamed the kfm - LASL_Passenger_car_v3.kfm. The downloaded files already contained a file called passenger_car_dummies_v3.nif, so I did not need to do anything to that file. The map I am working on just uses v1 and v2 files and the passenger_car_dummies.nif files are standard game files so I didn't need to do anything to those - the v1 and v2 files exist within the game as installed. If I had taken the standard dummies nif files and renamed them to say LASL_pass_car_dummies_v1.nif and a v2, then I would have to have a LASL_pass_car_dummies_v3.nif in order to use the new SF passenger car. You must have a version 1 and 2 kfm model and dummies file, plus whatever you are adding be it v3, vsf, etc. So much for the passenger car.
Bigboy_testmap1.jpg
Here's a shot of my test map files. I just added a folder under user maps titled V3 Passenger test and dumped the passenger files in it and renamed the kfm file LASL_Passenger_car_v3.kfm.
On to the engine. I created another folder under usermaps called Bigboy test and dumped the bigboy files I downloaded into it. I opened my RRT_trains xml file and added the xml for the Bigboy engine.
Bigboy_trainxml.jpg
There are number of things you can adjust in here - speed, power, year, etc. As far as getting the thing running, there are only a couple of things to worry about. I changed the <szCar> line to _v3. I added the <PassengersAndMailOnly> line, though I left it with a value of 0 (false), so it can pull any type of car. Change it to a 1 (true) if you want it to only be able to pull passengers and mail. You should have a routing image and an event_newtrain image. The game does not care if the image name matches the actual engine name, but the file you list must actually exist. Those image files are typically the last thing I do when I am working on a new engine. For testing I'll just list the name of some game engine or the name of one I've already tested, but whatever file name I put in those slots, the file must actually exist. In the case of the Bigboy, there is a tender to worry about. The image above lists the tender on the line below the dummies file. I like to put mine on the last line of the train listing, but the game doesn't care where you put it. The name listed must match the name given in the tenders section of the RRT_Traincars.xml. If it can't find it, it won't crash the game but the tender will not show up.
Ok. I made the adjustments to the xml files, which for me, only amounted to a few things - added the tender to the RRT_Traincars.xml, added the Bigboy to the RRT_Trains.xml file and changed the version from v2 to v3. I went into my RRT_Scenario_User_Practice_Run.xml (Practice Run is the name of my test map) and adjusted the eras dates so the Bigboy would come up right away. (I could have adjusted the <Year> in the Bigboy's xml listing and accomplished the same thing). I created a couple of folders under my Usermaps folder and put the bigboy files in one and the SF passenger car files in the other. Then I renamed the SF passenger car kfm to LASL_Passenger_Car_v3.kfm for testing.
That's all I needed, so I tried it.
First just the engine:
Bigboy.jpg
Then I told it to pickup passengers:
Bigboy_passenger.jpg
It worked! That's all well and good, but then I asked to to pickup another good at the next stop for which there is no v3 traincar - CTD! If you are going to use v3 cars, create a v3.kfm for everything on the map, as well as a v3 dummies file. You don't have to have v3 traincars, but you have to have v3 kfm and dummy files. You can take a v2 kfm and copy it and rename it v3 kfm so that the version 2 and version 3 traincars are identical. Do the same with the dummies.nif files and you're good to go. Or you can use v3 cars downloaded from this site, but you must be sure that the names of the v1, v2 and v3 files are all the same. If you are using the game standard v1 and v2 files for say manufactured goods, the v1 and v2 files are named Goods_car_v1.kfm and Goods_car_v2.kfm. Your v3 car for carrying manufactured goods must be named Goods_car_v3.kfm. It doesn't matter what the car looks like as long as it has that name. Likewise, the dummies file used for your v3 goods car must match the name of the v1 and v2 dummies.nif files.
I've never tried to do anything with a car version that wasn't numbered so I went in and changed the Bigboy xml <szCar> to _vsf, just to see what happened. I went into the traincar folder and changed the name of the passenger car kfm to LASL_Passenger_Car_vsf.kfm and gave it a try.
Bigboy_nodummysf.jpg
However, I forgot to rename the dummies file from v3 to vsf. Interesting that it still ran. I assume that it is using some generic passenger car dummies nif file. It didn't crash the game, but it wasn't happy with me. Anyway, you are bound to run into all kinds of errors. Some crash the game and some just cause errors or strange looking results. Some are obvious and some are just the devil to find. Usually, I have found that crashes during the "Building up Steam" portion of the intro, are caused by missing files. That may also be a case of a misspelled file name. As far as the game is concerned, if the file name does not match what it is looking for, the file is missing. It must be able to find the name as listed the the various xml files be they kfm files, nif files, etc. Capitalization does not seem to make any difference, but if your file name contains a space instead of an underline, the game will crash while building up steam.
Back to a few generalities. While I have not tested this, I see no reason why you could not run both v3 traincars and vsf traincars on the same map - but I'm not sure why you would want to. Each engine must be told in the xml what version of cars it will be running - v, v2, v3 or sf. Now you could have one engine pulling v3 passenger cars and another engine pulling vsf passenger cars and they might both be long cars. Heck, they could be the same car. You would just have to have both v3 and vsf kfm files calling the same nif file. The game just has a number of limitations built into it.
I know this is a lot to go through, but once you get a few basic ideas firmly planted between your ears, it's not too bad. The devil is in the details :>)