roof mount antenna center point

Does anyone know the center point of the access cab roof? I want to center an antenna. I've seen some body dimension diagrams floating around for the front and engine bay.

 

When I installed my through the roof antenna for my HF rig I took some blue painters tape and made an X across the cab from front left to right rear corner and front right to left rear corner. Checked it with my eye all around and it looked perfect. Center punched, removed the head liner, used a step bit to drill, installed antenna and head liner. It looks Factory as far as most are concerned.