The Navy was unhappy with the F-111B's tip-back angle. In other words, the main landing gear was too close to the airplane's center of gravity with the wings swept back, so if the brakes were applied while the airplane was being pushed back into a parking spot, the momentum would cause the airplane to tip back. This might also result from the roll of the carrier. And there were dire consequences: it might result in the airplane and brake rider being lost over the side if the tail skid was past the deck edge.
One early solution was a moment-carrying tow bar to move the cg forward. It was evaluated but determined to be inadequate, not to mention awkward to handle.
The decision for F-111B production was to move the wheels eight-inches farther aft.
I had noted that F-111B landing gear installation had changed at some point early on (probably with 151973 but certainly with 974 and 152714/5) to move the wheels aft.
The landing gear was definitely rotated more around the retraction pivot point, moving the wheels aft. However, a rough layout indicated that the shift aft was almost certainly less than eight inches.
Steven Hyre recently posted some F-111B illustrations on his Facebook page, The F-111 Historical Association, that were new to me. One of them was for ECP 1000 and revealed the planned change: