I was researching building a 1937 Cadillac Limousine with a weight of @ 5,500 lbs. Talked with the folks at Art Morrison who stated a MII based unit would not be stout enough nor be able to generate the braking needed for such a heavy car. They referred me to JFZ Customs that had developed a 1/2 ton truck based suspension using the truck spindles and rotors with a MII rack. The track width is 62" which just guessing is too wide for your application. They currently have an S10 based suspension in development.
Jim Meyer Racing has a suspension based on the second generation F body with a track width of 59" available. There is of course a weight difference between the Camaro and your limousine.
We were also considering http://www.pauzasfd.com/
who could design and build what was needed. You might want to check them out. Keep us posted.