this is a vacuum advance and retard .

you will have 2 pipes coming out of the distributor  diaphragm ?.

one goes to a pipe next to carb base and the other goes to a fitting on
the inlet manifold almost underneath the air filter box on top of carbs
.

you set the static ignition timing at a certain RPM , i think 750-850
idle  rpm and at TDC or 6 degs advanced on the front damper pulley
markings .

its been a while since i  had my range rover but it had same
configuration as you mention .

as soon as you touch the throttle you should see the advance kick in
and youll lose the timing mark when viewed by strobe light .

hope this helps