I have used ACSI-SCSI adapter board by Inventronik and tried with both BlueSCSI v1 and v2 on a Mega ST. An Atari ST(f,m) is the same so should work fine. But other/any(?) ACSI-SCSI adapters should work. Like Link2 and the other ICD boards (Advantage, Advantage Plus, AdSCSI). There is reverse engineered of those boards but I don't think anyone is making/selling them.