Dana 60 S60 or Ford 9"
You need to go talk to guys who are currently racing that type of car and pick their brains on how to build the car. I doubt that you'll find any serious racer recommending a Dana 60 for that type of car. You can also call a few chassis shops to talk about building a car like that and see what they say. I'd be surprised if any of them recommended a Dana 60 for that car.
Just because something is more popular, does not mean it's better or stronger. The vast majority of Ford users use the Ford for its ability to change ratios quickly or in case of breakage like Pittsburg racer has said. It has the most support of gear ratios as well. It has become ubiquitous.
A guy in the pits will probably have one to loan you.
Mark Williams website is full of explanations on why they have increased the diameter of the ring gear twice to improve durability.
They talk about there new ball bearing carrier bearings that work better under deflection.(Lack of Stiffness)
Prior to the s60 a standard Dana was a pita to setup requiring a case spreader that would be bulky to use in the pits.
The threaded adjuster feature was probably not available when most
Ss/ah cars were built. The Ford is lighter in overall weight, although the difference is largely exaggerated.
As I have posted earlier, Williams own website says the Dana is both stiffer and reliable than any third member type rear axle because of its one piece cast centre section, and much cheaper to build. The Dana with its 9 3/4 inch ring gear and the smallest
Hypoid offset of any of the popular performance axles is both stronger and more efficient than the Ford.
Anyone who has setup their own ring and pinion gears on a Salibury type axle will know what a great feature those threaded adjusters are in the s60.