I'm Heartbroken. Time to face reality that my Cuda is a parts car.

Squaring it up. Since your garage floor isnt dead level. No concrete pad is, you need to buy 4 bubble type torpedo levels, along with 4 good jack stands.

Remove the sill plates, then tape mount one torpedo level on each rocker panel facing front to back where the sill plate would screw down.

Set and tape 3rd torpedo level across the rear shock mount inside the trunk on top of the transition pan facing side to side.

Set and tape the 4th torpedo level across upper radiator support on the small ledge that faces the radiator.

Set the car on the jack stands putting 2 at the rear framerails nearest to the shackles. Put the other 2 jack stands under the front rails near the k frame. Then shim the jack stands with steel sheetmetal shims between the stands and body until all 4 torpedo levels are level. Now the car is level.

If the body and structure is really rotten, you probably need to strip as much unboltable weight out of it first before doing this.

Also remember, the dimensions these cars used since hand built in the 1960s and not computer robot welded can sometimes be off as much as 1/8" from the factory.