starter swap
 

will starter from 1993 taurus auto 3.8 fit 1994 aerostar auto 3.0

I may be wrong (wouldn't be the 1st time), but I'm pretty sure they are not interchangeable. The 3.8L is the 90° Essex engine and the 3.0L is the 60° Vulcan engine making the mounting positions different. You would also need to look at the nose cone of the starter, they are also most likely different lengths.