rear drop question

[76bonanza]

My rear drop is supposed to be 4 inches. I am redoing my rear drop because the PO used 4 inch blocks and I am going to drop springs. My question is I like the hieght in the rear but not sure how old the coils are now so dont know if it is 4 inch or not. I am running 275 60 15 tires and it sits about 30.5 inches to the high part of the wheel wells to the ground. Does this sound right? I just want to make sure 4 inch drop springs will leave me in the same general area.

Thanks for any help