A Post-WW2 strategic nuclear bomb (Mk III, Mk 4,6,13,18 - the 4 and up used the same shape) and so forth was 60" in diameter, 128" long, and generally massed in at nearly 11,000 lbs. (1.52m X 3.27m, 5000 kg), and required access to the bay so that the weaponeer could perform the in-flight insertion of the weapon pit, and finish the assembly of the explosive lenses.One of the things that did the Northrop flying wings in concerned the inability of the bomb bay to carry a nuclear weapon - at the time, they were big and heavy.
A note from the XB-35 Erection and Maintenance Manual (You never know when you'll find one in a barn) is this: Section IV, Page 13 section h. Bomb Racks:
"(1) Description,- XB-35 airplane (AAD 42-13603) is designed to carry to 500 pund bombs in each of its eight bomb bays. As this is an experimental airplane, the inboard bays will ordinarily be filled with special equipment making them of no use for carrying bombs. Since 500 pound bombs are the only type for which the aircraft is designed, the bomb rails, brackets, etc. ordinarily removable from an airplane are to be left installed, and should not be removed except in case of damage."
Given the the B-35/49 used the Northrop multi-cellular wing construction, the bays being nested in with the engine bays in the wing, it doesn't look like there were a lot of options. The Silverplate/Saddletree nuclear weapons modifications don't look feasible.