[Arran]

I think that McMurdo-Silver msut have used a better quality chrome plating then the contemporary Scott radios did. Half of the Scott sets that come up for sale have rusty or pitted chrome on them which leads me to believe that they only flash chromed their chassis. One manufacture that used very good chrome plating was Wells Gardner, it seems that most of the Airline and other private lable sets have reasonably good chrome on them even if the cabinet is trashed. In any even probably the best way to deal with that rusty amplifier chassis would be to bite the bullet, strip it down and have a chat with the local old car restorers about whom the best plating shop is for the money. You should be able to get a decent replating job for under $200 for something like that, and it's cheaper per item to get several things replated at once so keep that in mind.
Regards
Arran