I recently did a flush using Chevron brand Type F. It seemed fine to me - the PS system doesnt stress the fluid exceptionally.
I have run Redline synthetic in the other stang's PS system and it seemed to be fine (note that it explicitly stated it was for PS systems requiring Type F).
Personally I'd rather run a dedicated conventional Type F than a generic synthetic that doesnt state it's compatible (Mercon and MV have a much lesser coefficient of friction and you really want the bite of the Type F). It's easy enough to flush the system later on anyhow. I'd have recommended doing a flush before driving the car or filling it with synthetic anyways.