Then to fix it on the machine. Preferably with least dismantling of the machine.
An unavoidable first step is to remove the platen from the machine. Removing the platen knob (loosen screw) and pulling out the rod allows the platen to be wiggled out of the machine. (Images on a previous posting of April 2015.) Again a good idea to keep the line feed parts in place with a rubber band or such.
The machine then needs to be turned over, upside down. Obviously with the typebars flat. It is best placed on a thick wad of rags or an old towel to prevent damage and to not bend parts of the ribbon-reversing mechanism. (The ribbon reverse pillars can stick out and are easily bent out of shape, causing the automatic reverse to fail. I know now...)
Upside down, extend the carriage as far as it will go left and right and remove the hinge pin left and right. In the picture below is shown the carriage pushed all the way to the right, bringing the paper tray hinge in view. The rod may need a gentle tap from the right with an awl or small screwdriver to get the knurled end to protrude from the hinge. When it sticks out enough, it can be grabbed with pliers and gently pulled out, rotate and wiggle a bit and it should slide out fine.
Remove hinge rod at other side too and the paper tray will drop off. This also gives easy access to the paper feed rollers, both front and back. The front rollers assembly is merely held under the spring-rod and can even just be taken out. To replace or fix the rollers, it is however probably much easier to pull out the axle rods by the knurled end. (Don't pull the other end, that'd be the hard way.)
For re-assembly, the reverse procedure applies. The knurling of the rods being pushed into the hinge holds the rod in place.
The little Remington Portable then had a shiny and rust-free paper tray :-)
(Next up still is the lifting tray. That's much harder, as the clean replacement part did not quite fit. Some 'forming' of parts and frames will be needed to make it all work.)