Not sure of the application your needing but the Mustang/Cougar car C6's used about a 14" tailshaft. I can crawl under the car and measure one if needed. Most were aluminum cases but some high performance cars had the cast iron tailshaft case. I understand the 70's pickup truck C6's also had a cast iron tailshaft but were slightly shorter in length. I never had one here to compare to say for certain. I also don't know if the larger full size FE cars used a different tailshaft length. Hopefully someone can chime in on those. Just something to keep in mind with driveshaft length and possible future replacements.