umm, how so? I mean I guess a car 9" is narrow, but as mentioned you would have to do some sort of odd axle redrill or expensive aftermarket axles. Additionally I would not use a chunk from a car. With the exception of a few kick arse 9" car's all the chunks I have seen are small bearing and less than 28 spline.
Perhaps an EB 9" might suit you. Or I know, just get an 8.8, I have one from an '84 bronco.