Slide the floor out the end so you have all the pieces laid out.
The doors go back in the shell. I'm sure they're supposed to just be glued in. Use Canopy glue or clear parts glue, not CA so that it doesnt white cloud around the door.
It looks like you need to do a total re-wire and attach people back in the seats anyways, so you'll need the interior out. Use GRJs lightboard and some LEDs, a whole train of those cars will give a Z4000 breaker a run for its money.
Assemble in this order:
The superliner interiors are just screwed to a sheet metal frame skeleton inside the car. I guess make sure that all the screws are currently holding it together. Secure the shell to the floor with the pile of screws you have.
The trucks go back on by inserting the tab above the coupler in the floor, and securing it via the screwhole on the opposite (facing middle of the car) side of the truck plate. (The car will not slide back together with the trucks on and the shock absorbers mounted on the sideframes.)
The last thing to go on are the car ends, which just pop into place and are held to the floor with a screw in each corner.
The 2 triangular parts next to the left hand truck are the shock absorbers, they just pin into the sideframes of the truck unless the tabs were busted off, in which case, use glue.
From the photos, you appear to have a complete car.