Hi,
Many years ago I had a 1975 +8, with the old 4 speed Rover box. In every day motoring it was fine but as soon as you tried to rev the engine and then change up the box baulked. The noise was not very pleasant but was typical of the box - it was never designed for quick changes at high revs. I'd even had it rebuilt by MacDonalds and it made no difference at all. As I intended to use the car for hillclimbs and because of a slight (!) accident at Silverstone I changed the box to a SD1 5 speed along with a new 5 speed chassis. You could probably engineer the change with the old chassis but why bother. Keeping your car original will preserve its value and keep its original driving characteristics. Early original spec +8's are getting rarer every year so I would suggest if you want to change, get a newer car.
Paul
