Just to forewarn you it will be expensive and very laborious. You'd be better off selling the car and buying a manual trans gt. That said this is some things you'll need...
A manual trans floor pan section, the auto section will need to be cut out
A manual trans driveshaft, it's a different length from the auto
A clutch kit
You'll most likely have to cut the firewall to install the new pedals
The computer will need to either be changed or converted to a manual trans system
There's a possibility that you'll need to change the flywheel but maybe not
I left some things out but this all I could think of off the top of my head...
Adventure till you drop
Mustang of the day,
July 12, 2015