My opinion is if the engine runs well, plugs are not fouling with oil, and it only smokes while decelerating, it probably is a valve stem/seal/guide issue.

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