For years I have been trying to find a way to bring up corroded or faded ID plates made of aluminium with black lacquer infill.
It is impossible to recover them to new. The best I have found is to wash thoroughly with a good cleaner like Spray and Wipe with a soft brush like a toothbrush. Stop rubbing if you see you are removing any lacquer. When they are wet you will see they are much brighter and easier to read as the black lacquer goes dark again.
If you are anal about it you can get some fine sandpaper and gently go over the lettering (assuming it is raised with infill lacquer. Screen printed on a flat surface can not be touched). This makes the lettering stand out but takes care not to go over the letter edges and start removing black. Your Bedford main plate looks like it would come up pretty good with gentle sanding of the letters with narrow strips of fine sandpaper folded around the blade of a small screw driver and lots of patience
A couple of good coats with clear pressure pack paint will give a permanent wet look and also seal the corroded aluminium sections. Do the back as well to complete the protection.
At least with the steel plates you can see the data stamped but most of them seem to have the base information screen printed and once gone it is gone. I had some once with raised lettering and used rust remover and it worked fine. Don't use any aluminium cleaner as it will strip alloy plates clean removing the black lacquer instantly.
