Something I hope never to have to do...good luck with it.
Improving cooling on V8 Rover engined Mogs seems to be quite a common task and on he subject of cooling I agree that oil temperature is as important, if not more so, than water. The Rover V8s have a reputation for being marginally cooled: adding an effective oil cooler as David suggests will help keep the engine at the optimal temperature.
Idealy, so that warm up time isn't excessive, it should have a thermostatic valve so the oil cooler is out of circuit until the water is at normal operating temperature. An oil temperature gauge is also nice to have and arguably a better indication of engine temperature than a water gauge.
It is interesting that all the new small BMW engines have a thermostatted oil/water intercooler. On my 320i the oil temperature takes far, far longer to reach normal than the water, and unlike most modern cars it has an oil temperature gauge, not a water temperature one.
