It sounds like what I have -- except that I think that the gyro rotor is only 2" diameter. (It has been quite a while since I was last in there, and I never actually thought of measuring it.)
IIRC, it mounted by a threaded extension of the shaft on one end, and had three leaf-spring contacts on the three symmetrical button contacts. Yes, it was an inverted rotor design.
And if it is aircraft related, it will want 115 V 3 Ph 400 Hz power to reach full speed.
Really old panel-mounted gyrocompasses used turbine insets in the edge of the rotor, and were spun up by compressed air from the aircraft's motion, IIRC.
Navy gyros would be more likely to be run from 60 Hz, as the weight limitation would not be there that is present in aircraft. I've had various bits of Navy electronic equipment, and it was all 60 Hz powered.
But a gyro for an old aircraft could work from a small bottle of compressed gas -- CO2, perhaps.
Yep. If the bellhop knew what he was dealing with, all he would have to do is apply pressure at 90 degrees to the intended turn and it would turn as he wanted.
You could make your own, and have it spun up with a gas jet aimed at the steps in the edge of the rotor -- and you would only need a dividing head and an endmill to make the steps. (That gets us back to metalworking. ) Hmm ... maybe I should try my hand at making one. :-)
Enjoy, DoN.