For this experiment we're using the wheeled Duplo push and go motor block and red cabin from Set #10874.
The wheel width of the motor is the same width as a non motor base.
So, for this train to stay on the six stud track, the wheels need to sit either on the inside of the tracks or the outside of the tracks.
As the last picture shows, the wheels ...
Yes there is, and the standard is not unique to trains, but rather applicable to all LEGO construction. It is called MILS (Modular Integrated Landscaping System). You can find its specification in many places, but a good resource is at L-Gauge.org, where they have many more resources and standards for the LEGO train hobby.
From a train point of view those wheels will fit happily within the guides of the bridge, and the connections on the tracks should just about fit as well.
I'm fairly sure we bought our bridge when we were staying in a holiday cottage that had a load of the old black track, and it connected to the track successfully, but you may need to work with some curves ...
I could imagine that this design was chosen to take care of slight angular missalignment of the tracks at the peak of the bridge (the two parts are not exactly in a straight line but slightly bent at the joint). I cannot confirm whether this is possible, because I don't own these parts, but I think for easy assembly and disassembly they have to have a little ...
Warning: LEGO pieces were harmed for this answer
How the switch works
So, how does it work then? Well, let's open it up!
The back plate is held into place by 14 pins. We'll carefully pry it open with a knife. Alternatively, we could use a drill bit to slowly scrape off the pinheads.
Both methods are destructive. The back plate needs to be glued back on ...
Physically, these parts are compatible. They simply rest in between the rails. Various elements have made use of the space between the rails for years, such as points:
Older trains don't have any way to understand the function elements and respond accordingly, but they won't derail or anything like that.
Color sensor for some amount of time.
I was able to make green Lego tiles work, if the area I covered was 2x8 (in LEGO scale, not DUPLO) bumps. I put a standard Lego scale 4x8 brick under the Duplo track piece, and then built up the exposed area to the height of the center of the Duplo track, and then put 2 green Lego tiles (1x8) on top. This worked ...
Th easiest solution is to just use port "B" on the rear engine and then turn the "B" side remote control panel 180 degrees. They will then both go the same direction for "up" or "down". You may even find that having the rear motor 1 click lower than the front is advantageous so it isn't pushing too much in turns, trying to buckle the train.
You can attach second train motor to B output. However it will be controlled independently from motor attached to output A. So you would need to control speed for each motor separately.
Speaking of traction. The key thing here is your train weight. You might consider putting another full battery box (unpowered) into train just to increase weight and get ...
As seen in this video, it is possible to add Power Functions to set 7745 and run the train on gray tracks
Lego Train 7745 with Power Functions
photo from Brickshelf gallery
Lego 7745 powerfunktion
If the schematic you are asking is for the LegoDuplo, Train Push & Go Motor
with the circuit board that looks like:
This schematic is proprietary information that belongs to the Lego group.
This element uses a Bluetooth Low Energy radio and has an FCC ID: NPI28743
Perhaps you could create your own schematic and post it here.
There are numerous solutions over internet for attaching SG90 servo with LEGO. However I remember this particular video, which fit your need to attach/control Technic beams/liftarms. It also features required parts for this build at 7:48.