I had 2 Weaver brass engines. One was a mikado which I have since sold, and the other an 0-4-0 which I still have. I can't speak to the electronics since mine are 2 rail and I put my own electronics in them. They were straight DC when I got them.
Disassembly on my two is very straight forward typical brass. There is one long screw that goes through the cylinder saddle and attaches the boiler to the frame. There are two small screws at the back and bottom of the cab that attach the rear of the superstructure to the frame. most of the time the front screw is hidden above the lead truck which then must be removed first. Some brass locos have removable ash pan bottoms under the fire box which also must be removed, 2 screws each.
Mechanically again these are traditional scale loco drives. The motor is mounted toward the rear in the firebox with a drive shaft going forward into an Enclosed gearbox attached to an axle, generally one of the middle axles. The gearbox contains reduction gearing to allow higher motor RPM at slower speeds. This type of drive is in most Brass steamers. There is no gearing between axles. the side rods (connecting the wheels) transfer the power from the geared axle to the other axles.
They are probably different from what you see on Lionel, but I would guess not any harder to work on.
