COOL! I was a Fender dealer from '77 through '88 and we came to the conclusion that there were two totally different Bassman 10 production lines. Those amps either sounded great, or putrid. I've never heard anything in between. We even had two with sequential serial numbers that were polar opposites- we used both cabinets with either chassis, tried them into different speaker loads, swapped tubes, everything, and still one chassis sounded great and the other was awful.
Note that these are NOT the Bassmans revered by guitar players. By the time Fender developed these amps they'd determined that they were trying to make clean bass amps. The Bassman 4x10 amps that guitarists love were the original tweed ones (and reproductions) that had open-back cabinets. The Bassman 10 is a much larger cabinet which is sealed at the back and ported at the front, and had (slightly) better bass speakers.
As Downunderwonder says, "nice find". Enjoy!~
John