I think I would get the 55-57 kit from Waldrons, the chassis should be the same from 55-59, if you have to modify the front pipe to fit the 336 you at least have a good start and the rest of the pipes should fit in the stock location.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy