A heat exchanger (10) having at least one inlet tube (12) that ducts a heat exchange fluid (14). At least some of the inlet tubes (12) are characterized by a first cross-sectional profile (16). A core (18) is in fluid communication with the at least one inlet tube (12). The core (18) has one or more rows of core tubes that also duct the fluid. At least some of the core tubes (20) are characterized by a second cross-sectional profile (22). The first cross-sectional profile (16) is different from the second cross-sectional profile (22). A first endplate assembly (26) is positioned between the at least one inlet tube (12) and the core (18). The first endplate assembly (26) has a first section (28) that defines an inlet orifice (30) that is sized to sealingly engage the first cross-sectional profile (16). A second section (32) defines an outlet orifice (34) that is sized to sealingly engage the second cross-sectional profile (22). The first and second sections (28, 32) cooperate to provide a sealing engagement therebetween.