On my 1982 the measurement will vary depending on whether you measure to the top or the bottom of the instrument panel as it wider at the bottom than at the top. (ie its a trapezoid not a rectangle) Measurement from centre of aux panel to top...

I may be entirely wrong but surely Landrover would have used the same ignition switch/lock over a wide range of BL products of the same era and wouldn't have had the expense of a specific LR one. Maybe someone knows of a cross reference chart...

Most of the classic car guys I know use Woolies - they have a massive range of materials and trim and have been helpful to me when trying to source some out of run trims etc. https://www.woolies-trim.co.uk/