I noticed when restoring my '66 mustang my frame rails are about 2 inches different heights from the ground did anyone have this and fixes?

 

Front frame rails? Rear frame rails? How did you measure? Pictures? Where on the frame rails?

You aren't giving us much to go on.

 

could be the springs sagging. how did you measure?

 

rear frame rails i measured by taking off the whole rear end including springs and measured from ground to the bottom of frame rails

 

There is a possibility the mustang was on uneven ground or the mustang was at an angle on level ground.

 

what condition is the car in? Is there a lot of rust in the trunk floors, floor pans, and frame rails? If not did you find evidence of a past accident? It is hard to help much without seeing some pictures of the back of the car. If it was drag raced in the past it is possible to have a twisted inibody. Either way a frame machine is likely going to be needed to get it straightened out.