1. You do not need to worry about isolator bolts....the issue with those is on the '99 and newer windstars that use a different intake manifold.
2. The MOST likely cause of your problem is the EGR ports. P0304 is a missfire on cylinder #4. Your CEL will flash when this happens....
Cylinder #4 and #1 are the farthest from the EGR valve. The ports start to clog closest to the EGR valve.....so now most of the EGR gasses are going into cylinder #4 and possibly #1. Which is causing a missfire. Put a shop towel, etc into each passage below the EGR port....to minimize junk going on down.
The upper manifold gaskets are reusable.....I did replace mine....but did not need to.
You can buy new ones at
www.rockauto.com
4. You may want to remove and clean the spray ends of the fuel injectors. You will need to release the pressure in the fuel system....which can be done at the little valve at the center of the front fuel rail. I did NOT have to disconnect the fuel rail from the fuel line....I lifted it off of the injectors and set it aside. There is a clip for each fuel injector / fuel rail connection. Clean as much junk from around where the fuel injector goes into the head before removing the injectors....you want to minimize any junk going down into the engine.
You can do a search on EGR ports in this forum.....and find a lot of posts.
I have pictures of various repair projects for my '96 3.8L, including the EGR ports at
http://community.webshots.com/album/201931518cScpNK