The chassis is a relatively easy install under the car with minimal body/floor modifications. With the 9" rear end, the only mod that you have to make is a small channel in the rear passenger footwell for the frame rails to pass through. The picture below is in the early mock up stages of the chassis design. The green boxes show the area that needs to be modified.
With the IRS, there will need to be some minor modification to the corners of the trunk well to allow for the narrowed frame rails.