Daniel, the backstory is it started as a testbed for the K's powertrain, then had a fourth engine stuffed in opposite #3, and then the engines up-rated--not an all-at-once, but a lot of gradual tinkering kind of like a CH-53 version of how Dale Brown wrote his "Old Dog" having evolved as a series of improvements to the B-52. Standard E is about 13,200 shaft horsepower, stock K clocks in at 21,000, and this monster comes in at 40,000... if a buddy who's an engineer on the V-22 program and I are figuring right, it'd be able to sling-load a fully-loaded Strike Eagle.
William, a Pave Low package is part of it, and as noted I have an engineer working with me on it--we planned a second external tank on each side as a start, with an eight- or nine-blade main rotor to more efficiently use available power. We're also assuming part of the rebuild was extensive use of experimental composites, both increasing strength and slightly reducing empty weight. That extra power was part lift and a dash speed, but also with a capability to disconnect Engines 3 and 4 from the powertrain and run them as pure generators for a metric buttload of extra electronics. (Assumption: IF "adaptive camouflage" ever works, it's gonna need a LOT of power, both for the cameras and displays in the skin and for the computers to run it... and we're probably talking some beefy hardware there too.) As far as structure, the GE38 that powers the K is the same size as the E's T64, so not much enlargement there, the major challenge is redesigning the transmission cooler to make room for #4. Also, there was an operating assumption that Engines 3 and 4 wouldn't even be started unless needed for extra mechanical or electrical power--basically, the only times you'd see all four running flat-out would be slinging a loaded fighter (unlikely, but like C-5s crapping ICBMs a card in the deck available to play if needed) or in an extreme emergency where every last possible MPH is needed even if it means having to replace the entire top half the aircraft afterward--again, an admittedly unlikely scenario. Prevailing winds... onboard weather radar plus a satellite datalink monitoring NOAA's data?
You gents raise a lot of good points, some expected, some not quite anticipated, all appreciated.