yes, yes, & yes. All were Eminence Governors. I have a friend that has a 412 Marshall cab with the 8 ohm arrangement. And, my 412 Marshall is loaded with the 16 ohm arrangement. They are both in 1960B cabs.
Then there should be no difference in sound. Other than possible differences in individual speakers of the same type due to tolerances.
Does it make the difference where the presence control resistor (I think this is called the negative feedback resistor) is attached to at the impedance selector in the back of the amp? I have my Hoffman Plexi 50 wired up just like the diagram with the 47K.
It does matter where the resistor is, but doesn't matter if you're using an impedance selector switch.
That resistor is part of the feedback loop. The
voltage present at the OT secondary tap (8 ohms for the stock circuit in this case) is divided by the series feedback resistor (47k) and shunt feedback resistor (5k presence pot here), then introduced into the phase inverter. The amp was designed with the stock amount of feedback in mind.
Now if you have an impedance select switch, it doesn't matter what tap you're using, the amp still sees the same amount of feedback. There is a voltage present at every tap all the time. So, if you're using the 16 ohm tap, and the feedback resistor is still connected to the 8 ohm tap, both are getting what they need. In other words, don't think you need to move the feedback resistor to a different tap.
If, however, you had a multitap OT but the tap used and feedback resistor are hardwired to the output jack, when you re-wire for the 16 ohm situation, you are actually increasing the amount of feedback in the amp. You might then think the 8 ohm arrangement sounds "punchier" or "more raw". That's because there is more voltage present at the 16 ohm tap for the same power output, and when moved to the 16 ohm tap, the feedback resistors then pass more feedback voltage to the phase inverter.