I wouldn't opt for a Shaftmasters on any S197 Mustang. Sure, many will not have issues, but I sure did. No matter what the pinion angle was set at, the vibration over 100 mph would never go away. Every theory was tried, even a shaft rebalance by shaftmasters.
Replaced it with a Driveshaft Shop, set the pinion angle to -2*, and the vibration was gone.
The difference? DSS uses a rear CV joint that takes care of all NVH. Shaftmasters is using a slip yoke/u joint setup. The higher priced DSS is worth it. The two don't even compare in quality.
Don't make the mistake I did, having to buy twice....then selling my old shaftmasters (rebuilt remanufacturered) to a forum member.
Let's say DSS says the CV joint can handle up to 6 degrees of angle. That doesn't mean you shouldn't adjust the angle if you have 5 or 6 degrees. There is much more to pinion angle than at static ride height. As the suspension loads and un-loads it will change the pinion angle. As well as because of the axle rotation under acceleration and deceleration. Plus reasons like the way the suspension will work with a lot of negative pinion angle, large percentage of anti squat and so on. If you install a drive shaft you should set your pinion angle.
I just ordered a Dynotech from Lethal. They extended their Memorial Day sale through today so it's 75 bucks off. I'm forced to work an extra weekend this month so I can easily rationalize a marginally extravagant purchase.