This time arround ( for my Listeroid project)I bought an ENW 6KW brushless with AVR (that was the smallest offered) from akatosborne on ebay, only planning to pull 3.5 off the 6\1 setup,, My previous project to run entire house 24\7 12KW ST head would only put out 104 volts under even a light load, so I ended up with the expense of a modern AVR to correct it. In my case they, them or some bad builder, must have left out some of the exciter windings, I'm sure many ST's out there put out properly but not mine, anything with a micro chip in it hated the low volt power, even the water heater which had the fancy selector control for vacation, energy saver ,away selector would not accept the low volts and had to have it's brain cut out to function after WILMA turned us off for 9 days.
I don't have any issues with the brushes ( except the crappy holders) and thier function, in fact if my brushless develops a problem I'm screwed, if I was dependent on it, but my 12kw 1115 Changfoid is the 24\7 unit for full grid failure, AND I wanted bearings prepacked with synthetic grease (very smooth ans spins nice by hand) and an AVR to satisfy those nasty little microchips with constant voltage so they won't notice the HZ fluxuation so much, I'm hoping at least.
Metro Listeroid is currrently down to bare block for sand removal and machine work improvement.
However I believe most A\C units will run on anything from 208 to 240, all my 5 ton portable units at work are marked exactly that, check your information plate. With an AVR you could bump the volts and split the difference, 218 to 220 would result in 130 to 135 on the 120 volt legs of your 208 unit, ( that ought to bring the SR members down on me!)
But the AVR also gets rid of the third world rectifyer.
You would need to do alot of balancing with the 3 phase head you have or waste effecency.
But if the 3.3 KW per leg isn't a problem for you I'd use it.
BTW I think ST stands for STupidly simple, Beware the screwed together Chinese rectifyer!!
Bob P