LFS bass guitar cabs etc

Oh man, I have JUST the question for you!! I have a 70's guitar combo amp which I use with my basses - it's an FBT Jumbo 100. I bought it thinking it's a 100W unit, especially because it's kind of enormous. Turns out, it's a 10W mouse dressed in a T-rex costume. But... when I open it, I see it has a 12" speaker. I'm thinking I could replace the PSU and amp circuitry in it, as long as this 12" bad boy can output.
Here's the problem: the text on the speaker doesn't give any hint on what is its power. I would be very surprised if a 12" speaker could only output 10W, but I don't have much experience with vintage combo amp speakers. I suspect you may know a thing or two on the topic, though.
FBT_Jumbo_100_speaker.jpg