I believe they come with a 65mm or 70mm......i think its a 65mm.
Goto an autoparts website and look up Throttle Body for your mustang.....it will say the mm size.
BTW, DONT even bother upgrading to a bigger throttle body, this has been PROVEN a complete waste of money!
(think about it for a second...why get a bigger throttle body? That DOESNT change the size or flow patterns of the Intake Manifold, so it's kind of like increasing a pipe diameter, then squeezing it back down again, its truely pointless!
Goto ANY mustang message boards, they will confirm.
If you want to benefit from a larger Throttle Body, you MUST atleast Port your Intake Manifolds and Cylinder Heads first!
(which is alot of money....or alot of work if doing it yourself.)