GM (Chevy) Big Block Heat Exchanger.
MODELS CM454HO serial #89465 and up, TB454XL serial # 92882 and up, TB502XL serial #9 4268 and up and CM502XL serial # 88765 and up. Rear Mounted over the transmission. Removable endcap for service.
This unit is a direct replacement manufactured by Lenco in Long Island, NY, with genuine American Materials.