I think this was skirted a while back, 144bcd cranks first appeared on some complete track bikes in late1976 or early 1977, from Raleigh. The distributors still had and were selling 151's. Schwinn if I recall was assembling new Paramount track bikes with 151's as late as 1978, perhaps 1977 sold in '78.
So there was probably not a production overlap for the cranks, perhaps for the chainrings, definitely for the distributors' inventory.
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