I just happen to have done this swap a couple of weeks ago. Like the Post Above, if the 95 is a GT, there is not "much" difference. About the only real difference is the Oil Pan is "Slightly" different but you could still use the one from the FOX. The UPPER intake is definetly different but routing of the Hoses, Cables and whatnot should not be a problem if you wanted to just use the parts from the Fox. The Engine Oil Dip Stick Tube as well as the Dip Stick itself is different but again, use the one from the FOX.
I did mine so as to make it LOOK like it belonged in there and used parts from a Fox as well as a SN95 GT.
You will definetly need to re-use the 95 GT Wiring for under the hood. The Fox Wiring will NOT help you at all.
If you are working with a SN95 Mustang that HAD the 3.8 6 banger, you NEED A LOT OF PARTS! AND, I wish you Luck if this is your first such project.
Remember that in 89 their were quite a few differences between the HO 5.0 that would have been in Mustangs and the non-HO 5.0 EFI engines of other vehicles. Some will be roller, some will be flat tappet, some could have a 28 oz imbalance and not the 50 oz, as well as different water pump rotations and distributor gears. The water pump rotation also affects which timing cover you use... There are probably others I am forgetting. And that is all before we even talk about which engine your Stang came with.