With old cabinets like that, I wouldn't trust the label even if there is one.
Hook the cab(s) up to a multimeter and see what's going on in there. Also, your 190B should have 4, 8 and 16 ohm taps from the OT. If you need 16 ohms to make your cabs work, you just need to switch the jacks on the chassis around to make the outputs 16 and 8 instead of 8 and 4 ohms.
You might want to check the outputs on the 190B anyway just to be sure the switch hasn't been done already.
You know of course that the outputs are wired in parallel, right? If not, this means if you plug in one cabinet it will use that specific output tap (4, 8 or 16 ohm), and if you use both jacks it will default to the lower or secondary of the two used OT output taps (usually 4 or 8 ohm).
In other words, you can't plug a 4 ohm load into the 4 ohm output and an 8 ohm load into the 8 ohm output simultaneously, you would actually be showing the 4 ohm tap a 2.67 ohm load.
Well you could, it might be fine at least for a while. But you might eventually find yourself looking for a new output transformer, or power tubes and other miscellaneous parts…