For the X/Y conversion, you need a D--there's a lot of revision in the crop-tail rear fuselages... and even a D will need a lot of work, but it does get you closer.
Reengining: GO BIG OR GO HOME! I had actually pitched to a contact IN B-52 program management @ Boeing Wichita, after consulting a GE tech-rep, installing four monster GE90's uprated to 125,000# each and strengthening the wing to handle it. A StratoPig that can accelerate STRAIGHT UP?
As part of that, I had also endorsed the full Old Dog conversion (replace three-piece stabilizer system with a short V-tail, faster Concorde-style nose, total rebuild with carbon-fiber and other more advanced materials), but also adding the capability to mount a full second weapons pylon (maybe not as high-cap as the mains, but DEF not just a Sidewinder/pod rail as already used) between each wing's nacelles. Possibly reverting to the old 3000-gallon tiptanks and adapting them into a BUFF version of what the F-15 "FAST Pack" CFT concept was: "Fuel/Armament/Sensor, Tactical"--to include a Nemesis DIRCM on the rear of each.
A lighter empty weight, a heavier MTOW--and most importantly, the ability to rack up a buttload of air-to-air payload for those "When you need to close down somebody's skies and KEEP 'EM CLOSED" situations. Might be interesting to compare costs and capabilities of a theoretical "FB-52"-enforced No Fly Zone vs. one patrolled by F-15s...