I remember George Takei in a two part SIX MILLION DOLLAR MAN episode, where they went looking for the crashed plane of Steve Austin's real father.
That was only a one-parter -- "The Coward
," the second-last episode of season 1. But it was loaded with Trek guests, also featuring France Nuyen (“Elaan of Troyius”), Ron Soble (“Spectre of the Gun”), and stuntman/actor Robert Herron (“Charlie X,” “The Savage Curtain”).
Well, I only saw it once, and that turns out to have been 40 years ago. I guess it was only a one parter. Don't know why I remember it as two.