It's possible, but not easy or cheap. As above, use your phone or a Tomtom/ Garmin.
I've seen a couple of Garmin navs behind an OE trim panel.
Something like this in a D3, which is a 6" Garmin in the lower spec model's storage cubby, behind a D4 audio system bezel.
56 plate HSE? Is that not a DiD rather than Range Rover? In which case whatever works in a Disco is more likely to work, rather than the nightmare that is replacing the L322 system. @gstuart any insight?