How difficult would a 16-inch F3 conversion be?

Could the F3 design have been modified to carry Britain's 16-inch/45 guns?

Yes. The barrel dimensions were close enough that the conversion was technically manageable, though the turret and internal gun systems would still require redesign.

Nominal caliber lengths put the 16-inch/45 barrel about two and a half feet shorter than the 15-inch/50. The calculation is a reminder that a larger bore does not automatically produce a longer weapon when caliber length changes. Turret width, breech arrangements, ammunition, and internal mechanisms would still differ, so the change was not literally interchangeable. Even so, the basic F3 hull and mounting concept could have been adapted without redesigning the entire ship.