they are basically the same but the headgaskets differ year to year as they swithed from graphite to mls style gaskets slight diffrences in the blocks wont alllow the mls gaskets to swap to an ealier block.
The big difference happed in '99. When Ford changed the 3.8 from single port intake to split port intake. They also revised the HG's for the last time and it cured them from blowing. Power output was also changed, i think from 150 hp? to 190 hp.
There are some key differences from a '95 and a '99, just i am no too keen on the differences