the major diff between the two 413,s is the heads, if you inspect them the industial heads dont look anything like a set of street ones(452,906,915, etc.) Iaso believe that the reverse rotation cam was only on boats with twin engines 1 stbd 1 port the reason is for coter-rotating props. and ive seen both types of carbs on these TQ,s and carters(not sure what years) and a holley also.