rear upper shock mount extensions

I have done the same thing, moved the rear axle aft, and the only way I can see that you will be able to move the upper shock mount aft would be to cut the upper shock crossmember out of the car, along with that portion of the floor, and weld it back in where you need it. Or you can do as I am doing right now, weld in a coilover shock crossmember and mount the shocks in front of the rear axle.