While the copyright date on box says 1977, it's more likely to have been released in 1978.

Consisted of vinyl suit and thin plastic mask. Packaging was in an 8.5" x 11" thin cardboard window box with color artwork and logo.

From StarWars.com:

The first Ben Cooper Boba Fett costume (there were two) holds a special place in the galaxy of Fett collectibles, as it appears to resemble early marketing illustrations for the 1979 Kenner action figure. In fact, the costume itself seems to show a depiction of the action figure, complete with red rocket firing missile in his backpack. This Fett will cost you far less than the action figure, though — these can still be found complete in the box for around $20.