Tyre pressure

when I got the vehicle somebody put Range Rover 18's with road tyres on my D2 .
I've been told that they are the L322 ( if that's the right style ) and the size is... 255/70/18

I'm now wondering what kind of tyre pressure I should be running with 80% of my time on normal roads.

I can't find a guide for mix matched wheels/vehicles

Tyre pressures ar largely decided by the weight of the vehicle and not the size of the tyres.

With a D2, the recommended pressures are 30psi in the front and 38psi in the rears. After that and just to be sure I would try the "Tyre pressure chalk test":-

https://www.landyzone.co.uk/land-rover/tyre-pressures-chalk-test.274005/