Good point daredevil! In 1959 the 383 started as an "RB" Engine, with a dual 4Bbl intake that produced 345 hp, However this casting, 1827899, was used for 1960-62 which was a 343 hp motor. From 1960 - on it was a "B" Engine. I also bolted this on to a '69 383 and it fit like a glove. Thanks for pointing that out!