Now I'm not an expert on this, but from memory the real wood was only available in walnut. And looking at Rimmers, I reckon that the change to plastic takes place at VIN (Vehicle Identification Number)
238546 (Please don't take my word on this).
So from that VIN
, it's an early real wood car, which must be walnut. (I reckon)
Anyone agree on this theory?
Not sure there's any other way to tell from the info you have, but the wheel should have a part number. And always remember, someone may have put an oak wheel in a walnut car, as they were relatively cheap at one point and looked OK.