I got some Caswell stuff & plated the covers.... it's ok but not great. the radiator cover and most of the nuts & bolts that look copper were soaked with a copper sulphate solution you can get at stained glass supply. it actually puts a plating of copper on lead, steel, and even some stainless. it reacts with zinc & cad plating though & turns black. the plating has to go before you get the copper look. I've been burning it off & hitting it with the wire wheel (obviously, do not breathe this stuff) actually, you can just soak it & keep buffing it until the copper takes. then polish it with some Mothers billet polish...
I always tried to use brass hardware when possible but it is getting harder to find... it's all turning to plated steel, and I don't think the plating is even brass because it looks wrong. BTW, there is no metric brass. I converted to SAE where possible & helicoiled the brass dome nuts where metric was required