Cleaning Dataplates

[KiwiKev]

I realise its not a CMP or even Commonwealth based however the best overall knowledge seems to reside here, so hence my questions.
Recently I picked up my latest toy a 1940 4x4 GMC ACK352 ex USMC.
My question is how do I clean the dataplate to make it more readable, and look presentable.
The plate is an aluminium plate with black face and slightly raised aluminium letters for the categories with stamped blanks areas for the data, if all that makes sence. If you wipe the surface with a damp rag it cleans it a little for a short period of time, the clouds back over.

Also as it's a different plate to the nomal 6x4 / 6x6 GMC's does anyone know were I would go to have a reproduction one made?
Below is a photo of the truck

Regards
Kevin
Auckland New Zealand
Too many Rovers and not enough space for the real MV's