Inverters, it would appear, were not uncommon. I get the feeling that the quality of the (unregulated) AC from alternators was insufficient for instrument applications, and was primarily used for less sensitive systems. For more stable AC, it appears that the inverters were used.
Alternating current for the autosyn instruments, drift
meter, radio compass, and warning signals transformer is furnished by
either of 2 inverters, one of which is a standby for the other. One
inverter is under the pilot's seat and the other under the copilot's
seat. A single-pole, double-throw switch on the pilot's control panel
controls the DC power to the inverters and selects the inverter to be
used. In the "NORMAL" position the left-hand inverter is on and in the
"ALTERNATE" position the right-hand inverter is on. Source
Anecdotes on PPRUNE also seem to offer support for this.
Finally, a decent source. Two (unregualted) AC alternators for 'windscreen deicing and some radar equipment', with 2+1 spare single-phase inverters for other AC users.
Has 6 generator dials, and 4 inverters on the flight engineer's station, looking at a panel diagram and the bottom right of this photo. That being said, there are two switches labelled alternators on the AC section of the panel. They only seem to offer "NESA Bus" (B-47 manual seems to imply this is for window deicing) or Bus No. 2, depending on how the right switch is set. The left switch is for the voltmeter/ammeter dials.
Credits to brewbooks on Flickr