Well,as far as I know the Mustang has the same neck pocket as other Fenders,so it's no problem to swap the necks. Just be aware that you might need a 4 bolt neck,so don't look at used '70's era jazz necks,because they've got a 3 screw neck. (it is fixed with 3 screws,instead of the 4 can be seen on the jazz basses nowadays)
Hope it helped!
Have you looked at All-Parts,Warmoth,and other manufacturers to get the right neck for you?