Barry,
not sure. I know that in 1991 the plus 4 moved to the plus 8 chassis.
However in "Morgans to 1997" by Roger Bell it states that the 4/4 ran on either 165/15 or 195/60 tyres.
It also states that the 87 plus 4 ran on 195/60 tyres.
Maybe you could ask the factory to comment.
Good luck.
