Many thanks to all for your replies. I think I will sand and repaint it. Rust is very deep and I found some under paint. I already buy some new plates from sew classic, they were not too long but a little bit too large and after a little grinding they fit perfectly. The plastic one is also a good idea, I must find some acrylic glass but the one I could find locally is a little bit thinner.
I will post photos of this restoration here, but first I must finish a 48K.