You can try
www.dvsretorations.com for installing the cobra IRS in the rear. He is one of the best around for this type of install, very nice guy and most importantly honest. His website is down at times but you should call him. He sells all the proven bracketry and small parts needed for an individual to easily install themselves.
The watts rear suspension from TCP is being revised, so I would wait for their newly revised system for the rear instead of looking into the present one available. Here is a link that will let you know what is out there.
http://www.nzmustang.com/Newintoold/newintoold.htm
The latest out there for Mustangs is from
http://www.rrs-online.com/ , they have some trick suspension packages for the front (no upper arms, mcpherson strut design) and a nice 3 link + torque arm kit for the rear.
You can easily go 8.5" on the front if you nail the backspacing, roll the fender lips, and have tubular control arms. On the rear, you can go up to 10" wide if you roll the fender lips. I am installing 255/18's on the front and 285/18's on the rear of my 70 Boss 302.
For the steering, if you are going to trade the ram pump for a rack, I would go TCP. I have had the best results with their rack.