The spare, boxy lettering style and woman in BG104 are identical to those in BG103, but the fare couldn't be more different: rocking blues vs. Big Brother & the Holding Co.
The postcard was printed before the concert. It measures 4 1/2" x 7".
There were also some pre-concert double-sized mailers printed that were conjoined with the BG103 image (see BG103/104). They measure 4 1/2" x 13 15/16".