Magnum Mania!

This is is a screencap from Echoes of the Mind. Excluding any 'Nam era flashback sequences, and his post Echoes of the Mind drinking phase, was TM's hair ever as long as it was here during the show?:

It just may be. It gets a little mullet-ish in the seventh and eighth seasons but the party in the back doesn't get a long as seen in your shot.

Including flashbacks, however, the longest is most certainly in Dream a Little Dream.