The first one looks like a GM recirculating heater, which only had a cut-off valve at the water neck. The second is a fresh-air heater. Both were available from the factory or to be dealer installed on a new truck. Neither "should" or "shouldn't" be there, as either was available from GM.
www.oldgmctrucks.com has a '54 GMC accessory manual online, most of which is also applicable to Chevys - both heaters are also shown in the Chevy accessory installation manual available from any of the parts suppliers.
On second review, that isn't a standard truck recirculating heater, which used a round heater core. The front case looks the same, the back is different. It may be from a car? Anyway, it's definately GM and from the right era.
