I have a pair of these cabinets which look like the 1958 PM magazine version loaded with Electro-voice LT-12 drivers.The LT-12's are 12" with whizzer cones and the cheaper T-35 type horn with internal crossover.
I measured the LT-12's installed in the Karlson cabinet and they play nicely down to approx 60hz(fs of LT-12) which is okay if you use a sub.
Efficiency is approx 94db/watt by my guesstimation.
Local pickup in Columbus, Ohio as they would be difficult to ship.
Asking price $450.00 or possible trade for tube amps/JBL or Altec drivers/wood horns.
Regards, Ron