while trying to install the power steering drop bracket I broke the end off the stud you need to hold onto to turn the nut off. so I need another....are there any cars that interchange with mine or am I sol and need to order another

 

If you mean the shaft on the power cylinder, the only one that's the right length is the 67-70 Mustang and Cougar. If it helps any, they are available new.

 

do they just sell the shaft i thought i had to buy a whole new unit

 

Yes, you have to buy the whole cylinder. It's a different length, depending on which car it's used in.