I like my datsun backfires
If you want to stop the backfires, all I can say is that it will be difficult. The usuall cause of this is excess fuel in the exaust when backing down from high rpm. Leaning out the carb will help, but may make it run hot or lack power off-idle.
My best advice.......learn to love it.
72 Datsun 510
built L20b race engine
dual dell'orto DHLA 40's (no wonder I have backfires...)