The Metro Turbo came fitted with an oil cooler as standard.
I do not currently run an oil cooler on my car {though power output is almost double that of the Metro} as I've found that the oil doen't require one.
Oil which is to cold is as bad for engine wear as oil which is to hot.
After fitting a gauge as pictured below, & monitoring the oil temp it seems an oil cooler just isn't required. Normal oil temp is only around 80deg, even under harder driving, which is fine. The only time any real temperature is reached is on long motorway journeys. But even then it only reaches around 100-110deg. Modern oils are more than capable of coping at these temperatures, so the oil cooler is not fitted.
I would advise fitting a gauge & checking to see if your engine really needs a cooler before fitting one. I suspect for track cars or people who drive their cars hard for very long periods one may be required.

Oil temp gauge.

Adaptor fitted into sump {speedo end} for temp gauge.

I picked this little oil cooler up at the scrap yard for £5.
But make sure if you buy secondhand that the inside of the cooler is thoroughly pressure washed out, they're usually full of crap !

I currently run the Millers CTV. I've not stripped the engine since running this oil so cannot comment on how well parts have worn. But will update when I have.