Hi Dallas,,Here is a link to the rear end swap.. In link they are stating 66-70 housings are the same width.. There not 66-67 are narrow than 68-70.. The 66-67 works best for clearance.. you get big bolt pattern and a wide tire underneath.. http://www.hotrod.com/how-to/transmission-drivetrain/mopp-0404-8-3-4-rear-axle-housing-swap/