LO and others,
I think that Rand were tasked to do a study into USAF tanker configuration options - worth looking for.
I believe the conclusion was that it would be effective to swap smaller tactical aircraft over to probe and drogue and leave boom refuelling for large aircraft, but I am very prepared to be proved wrong.
What I do know is that replacing the A's boom receptacle with a retractable probe (as per B and C) would save a lot of weight (around 200 pounds plus) and give back a good amount of fuel (over 400 pounds). That's good numbers for a tactical fighter bomber.
Best Regards as ever
Engines