While the presentation is kind of a wall of text, in-game presents the best place that this information could be provided. While the AdvTrains train catalogue tries to do its best at providing information on all train content that is available, it is subject to becoming out of date as well. With this mod installed, the information is generated from the actual data of the train as it was registered with AdvTrains, making it impossible for it to be out of date.
A great feature that is included is a 3D preview of what each wagon looks like that can be orbited with the mouse/touch controls. Finally, you can find out what the bottom of every train looks like. I know you want to.
This is billed as still a Work in Progress, but there are only some minor improvements I would make: some headings, since variation of the text size helps navigability, and maybe some kind of split between more basic and more advanced information sections. Also the use of proper item names instead of itemstrings and give the speeds in the internally-used m/s (this is the unit technically already used without being named; technically a node per second is only a m/s by convention, but anyway..) as well as km/h and maybe mi/h (mph) if we want to be generous.