Tom. I can't comment on the M3W as I have only had a short drive in one. We have a Plus 4 and since March 2012 we have done 55,000 km. We use it for long trips and touring. The main problem has been getting

not to pack for a month when we are going for a week, a task at which I have been totally unsuccessful

Despite what others say we have found the car to be reasonably waterproof and the addition of some neoprene in a couple of points has resolved any problems. (Thanks Dave)
The seating position for me is very comfortable and I can drive for longer distances in the Morgan than any other of our cars.
Regarding the smaller steering wheel: I have fairly long legs but not as long as yours, I must admit. If you fit a smaller steering wheel you may like to consider having power steering fitted. The Plus 4 without power steering is a little heavy at parking speeds and a smaller steering wheel would mean much more effort would be required. The other alternative would be an offset steering wheel such at this:
https://www.moto-lita.co.uk/steering-wheels/offset-leather-wheel/
Or alternatively a custom wheel with a flat bottom section such as on the new VW Polo