In his autobiography, Kelly Johnson basically said they had a long engine to fit in, the turbocharger and it’s associated plumbing, the landing gear and the cooling system. And by the time they had found room for all that they were out where the tail could be-so they just stuck one on!
Incidentally, he went up with Hughes in a Constellation when Hughes was shopping for his TWA airline and the pilot let him fly it for a while-and at one point the ASI read ZERO! (The first and only time Johnson and his team had seen that while flying!) So they got him out of his seat and landed back in silence!