I think the actual JBL's came in the Peavey Session 400 and LTD 400 steel guitar amps, probably circa '74-'77. The good black widows have the spider web sticker on the flat magnet. Eventually Peavey thickened the paper and they never sounded quite as sweet as these early black widows. The good 12" black widows can be found in the Peavey Artist amps. Those were often 1-12", 80 watt tube amps that were sort of Peavey's attempt at a Boogie combo. I think there were 15" versions too. Pretty good sounding amps IF you get in there and put some real bias on the power tubes. Stock, Peavey ran the tubes way too cold and safe and power tubes just don't sing until they're biased right. Peavey did it as a low-maintenance factor, a fixed cold bias, never worry about it. But the tone suffered. You can find these Artist amps real cheap. Look for them, they're out there.
Also, I believe that the orange D120F and also the 15" counterpart, the D130F speakers were slightly different than the older, original D series. The "F" stands for Fender, and for Fender they slightly widened the voice coil gap so the speakers could handle a bit more heat and abuse in a guitar amp without rubbing. Then, I think, the K series was built on these "F" frames with that slightly bigger voice coil gap. There are some people who swear by a true original D120 or D130 because the tighter gap made the speaker a bit more efficient and tonally more nuanced. But they do blow quite easily, or if they dont' blow, heat can warp the voice coil just enough to begin rubbing in that tight slot.
I've been using a pair of orange D120F's for over 20 years. I always refer to them as K120's because the recone kit I had put in back in the '80s were "K" kits as I understand it. And since the K frame should be the same as a "F" frame, I just call them K's. They're still rockin' after 22 years on these same cones.
... and it's just like any other day that's ever been...