Here is a typical vintage 49-53 heater your bronze color scheme would be correct.
http://www.flickr.com/photos/advance-design_parts_co/8129343557/in/set-72157631868452754
Here is a NOS GMC for comparison, most of the spray colors I have found are closer to this.
http://www.flickr.com/photos/advance-design_parts_co/8129439492/in/set-72157631868452754
I have a recirculating type so painted mine like this,I have had good luck with the Rustoleum Hammertone. My advice when you find the color is go 3 very light coats to keep the Hammertone effect close to stock.
http://www.flickr.com/photos/advance-design_parts_co/8129058715/in/set-72157631867396207