I've seen other 55 Fords and it looks like these are supposed to be shiny chrome, but I could be wrong and that might be aftermarket. Does anyone know if these are chrome because they look like they're just aluminum or straight steel?
I'd like to give these some TLC and see if I can get the stains out and get them shined up, but not knowing the material I don't want to mess them up. Anyone have any suggestions what to use?

Remove them and use chrome/metal polish and buff them.  They will come back alive and look nearly new.  After using the chrome polish, use a good paint polish and buff with soft cloth.  Joe-JDC

JDC

New reproduction "scuff plates" are available from Concours Parts for $149.95 for the pair. 

Most that I have run across are aluminum

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

When they were new they were shiny bright Aluminum. Here is a product that I use. Pre-Treated with Polish and cleaner. Won't cause Scratches etc.

  

Thanks for the response guys, I'll try it out this weekend and post some pics of how it comes out.