three phase power is fundamentally different from single phase, which does not transmit constant power.
in anycase expect to run those microwave TX's at around 1.2-1.5 volts per hz, not 2 v/hz.
it might be practical to get 500 watts maximum through each one, peak efficiency will probably be lower, around 300-400 watts.
so, nominal voltages would be more like 90vac in maximum, and 1600v out.
you'll have to pull the magnetic shunts out, and i would fill the space with more copper, but that's not strictly necessary.
anyhow, what do you want single phase ac for?
you can't convert 3 phase to single phase without something to dump the energy into, and pull it out of.
running an induction motor off three phases and only pulling power from two of them is one way to do that, but its not very efficient.
you can convert 3 phase to two phase with a scott-T transformer, but there isn't any point in that either IMO, unless you only have two transformers to work with.
you will have to make three x single phase, or a three phase battery charging step down transformer.