Leonard, I can see where you're going with this.
Polished brass radiator tops are very nice but AFAIK they're painted black for a reason.
I've been led to believe the black is to aid heat dissipation, the same reason VW Bug engine tinware is painted black.
I worked for years on Air-cooled VWs and we had a number of guys had 'blinged' their engines up with chrome and consequently had overheat problems.
I'm not sure how it would be in a water cooled situation,hopefully someone will confirm my suspicions.
Just my 2cents.
