Oil coolers are a good idea especially if you regually push the car to its limits, i have one on my Truimph Toledo. To fit one You would need a spin on addaptor that screws on where the oil filter is this has two pipes to which you can attach the cooler. The Oil filter screws on to this.
an example: http://www.rimmerbros.co.uk/rimmer/triumph/dolomite/accessory
the down side is the oil may not reach its corect running temp so will not provide enough lubrication thus damaging the engine in the long run.