This is why you do not tell them to use these 2005 mustang specs, it will confuse them more than they are now. Never get half of that caster spec on a stock suspension.
I disagree, but certainly your mileage may vary. When they fail to hit that spec, you look at the numbers, thank them for the effort, and walk out of the shop with maximum positive caster. Even if it is half of the mustang spec, its more than the stock specs, which will achieve a better driving vehicle, unless you insist on using F70 bias plys under your car.
There is no reason why a tubular upper arm suspension, which the OP has, can't hit those numbers and there are some on this board who have achieved more than that.
