mrragu

Hopefully the title got somebody's attention!!

I have (wife and I bought my son) a 2000 Mustang GS. It has a 327 rear end and we (me and my mechanic buddy) think we ought to replace the rear end. I have found one used off of an upgrade a guy did on his 2005. The '05 is a 331. Questions:
1 - Is the bolt up for the '05 same as the design on my son's '00?
2 - What does this gear ratio change do to me?
3 - Isn't the '05 and up a true coil over strut design and what does that do to my separate coil/strut situation? Would I need to buy that crazy expensive coil over conversion kit?
4 - Would it work without refabricating the back of the car?

Any help would be greatly appreciated.

Mike