In response to reverse flight question, according to wikipedia the bigger tail rotor came out with the B206B-3.
JD
From wiki:
Bell 206B-2 - Bell 206B models upgraded with Bell 206B-3 improvements.
Bell 206B-3 - Upgraded Allison 250-C20J engine and added 2 inches (51 mm) to tail rotor diameter for yaw control.[