I am not familiar with that particular model, but have to assume that it isn't that much different than newer models when it comes to G53. So I have a question. Why are you using G53 to move your work shift? G53 is suppose to be machine home position as far as I know. I don't use it except for my subspindle (B-axis). The command G53B0 sends the subspindle to machine home regardless of the work offset being used (G54 thru G59).
I have to think that by increasing the G53 by one inch you are telling the machine that the turret is one inch further from wherever Z0 is located on the spindle. Thus it moves in an extra inch. This is similar to how the work shift works on our Hitachi. There is no G53, G54 etc. Making the work shift larger makes the part an equal amount shorter. Add a minus number to make the part longer.
Edit: I'm quite certain that the large reading for G53 when it is used to send the turret home is because that is how far the turret is from the machine's Z0 on the spindle. I think you are confusing the turret's home position with the machine's Z home position.