This is the fresh air optional heater for the 48-50 trucks. The 51-52 were different in shape, but operated the same way. As for color, you can use "Ford Argent" paint which Ford used in the 70's thru mid 90's for a match. Any Ford dealer can order a can and get it next day. I took my heater apart and it's a dead ringer for a match.
THere have been a few threads on here lately about your style heater. Do a little research in the archives. That heater is not correct for your truck if you're doing a proper restoration. But, back when these trucks were new, few came with a heater installed from the factory. Most were dealer installed ( profit maker ) or customers went to Sears, Montgomery Ward, Firestone, etc.. to buy a heater because they were much cheaper. These were work trucks and people didn't spend alot on thier trucks.