Given the other artists included (especially Miller/Janson clearly in their DARK NIGHT phase), I'd place this around 1986. Honestly if it weren't for the signature and other vintage of the other pieces, I would have mistaken JB's piece as very early Walt Simonson - those crazy slick curved lines were his trademark back then.

Late ‘70s might preclude Truman & Adams, and the “6” in the corner might literally agree with the 1986 timeline.  I also don’t know the character, but wonder why Truman went with a more Zorro cordovan than the bowlers—all very interesting!