OK, I hear what you're saying, but surely fitting the new gear into the E-3 airframe is no more than an electronic refit? You've got an electronically hardened airframe which is bigger than the C-135 so making it physically fit should not be an issue. As for the wiring / databus - well that would have to be retrofitted whatever aircraft you choose
You don't need to do that much metal-bashing surely?
However if theres only one in mothballs then the question is academic anyway - I was under the impression three had been mothballed by the recent cuts