Rowler there should be a part number stamped on the aluminium casting around the pinion, probably under some dirt.
There's also a service sticker somewhere on the car that will tell you. On 1980 models I think it might be in the boot, on the back edge of the boot opening, near where the hinges are. It looks like this:
If you do find this sticker, report what steering-gear code you have here and I'll look up what rack it corresponds to.