It states right in the owners manual that 89 octane is the norm for the 3.8 motor.
This is not a supercharged or turbo charged motor requiring 91 octane or higher.
As for the cats, the new ones are installed and she seems to be running better.
If the Windstar does not have a throttle body, what exactly does it have. I would be under the assumption as I am mechanically inclined that the throttle cables from the fuel pedal are leading to what we know in the industry as the THROTTLE BODY. I am not aware of any other terminology for these air controling meters other than the terminology I have used.
You have the air filter, the mass air sensor and than the throttle body where inside you will find the butterfly where the throttle linkage will be hooked up to in order to control air flow and desired fuel | 
