That Alpha 6 is late '70's early 80's, and that speaker looks to be same era. Wouldn't have a factory installed JBL for sure, probably a Model 6 rated @ 100 watts and 8 ohms.
In the last regularly gigging band I played for, I sort of used a PA speaker for stage volume. I mic'ed a '68 200S into a Sonic I40 cab with a K140, and took a monitor feed from the board into a JBL PRX812 pointed at my head. The rest of the band was on in-ears. I can't get into in-ears myself, I don't seem to play as well when I can't get that organic audio bond with the drum kit and audience interaction.
So I had my bass on one channel of the PRX and and a FOH feed on the other input, and I could mix and EQ the monitor with my iPad.
I'm on board and in agreement with Isaac's comments about overtones above the response curve of most bass drivers, but I gave up on compression drivers for bass decades ago. For me personally, there's really nothing up there that adds to the tone I'm looking for from a bass guitar.