This is really “slaving” the gamma driver to the alpha driver, rather than Z to X, from the perspective of smoothieware. At least one way is to disable gamma step, dir, and enable in config.txt (leave gamma_current correct), and use a jumper to connect STEP, DIR, and EN from the alpha driver to the gamma driver.
@Arthur_Wolf I don’t see config.txt options documented for configuration-drive axis slaving. Did I miss something?