i think the cobra IRS is going to be too wide for the first gen mustangs. from what i have seen the cobra IRS will fit the 67-73 mustangs, but you are going to have to make your own mounts. do check the location of the front spring mount son the early car and compare it to the length of the fox body lower control arm. it seems that ford used the same front mount for the IRS in the fox 4 chassis when they created the IRS cradle, and it seems to me that except for the angle of the mount, the front leaf spring mount is in the right location distance wise to help mount the IRS cradle.