Luckily we don't have MOT's here, so that's not a concern.
Just like where I live now, I feel we are truly blessed, makes a whole heap of difference to the ownership of older and "special interest vehicles", as the world used to be in the "good old days, when I were a lad", but I only bought D1 Disco's without air bags and no ABS, don't even have a radio or cd player.
Not sure if it would be easy to get a steering wheel hub to suit an aftermarket smaller wheel, I did look on line for one for my first D1 and decided I would probably have to make one out of the centre of a standard Disco "S" wheel to get the right spline, I have done this for a few previous vehicles where there was no adaptor hub available, not sure what is available in your part of the world.
I have a late 60's "Les Leston" brand 13" leather bound sports steering wheel still in near perfect condition that I originally bought brand new to fit to my '62 Austin Healey and have had fitted to about half a dozen special, (to me), cars I've owned since, (including a BJ42 SWB 'Cruiser), never let it go when the cars got sold on, I would love to put it on my current '98 D1, think I will make it a project, thanks for the reminder.