An update and extra info for anyone who is toying with the idea of new seats in their Morries (sorry Moggies -- we call them 'Morries' in Oz).
I have the 9-5 seats now. They look excellent. They have leather facings, up/down adjustment, tilt adjustment, lumbar adjustment, and the usual fore-aft and seat-back angle adjustments. They also have heating. And they have side airbags--which are totally useless in a Morris.
I just hope I can get them to fit! The Morris and the seats are in different locations at the moment, so I can't do a trial fitting.
Further to Andrew's very helpful measurements (on the first page of this posting), here are some measurements of the mounting rails:
Distance between rail centres: 42 cm (looks a bit wide for a morry)
Rail length: 39 cm (both sides)
Mounting hole separation (fore-aft separation): 34.5 cm.
The mounting rails sit flat on a flat floor (if that make sense). I hope this will simplify installation. It also means they make nice lounge chairs

I have already given them a trial in my spare room.
Something for Moggies with standard power units to keep in mind is that with all their paraphernalia, the seats are quite heavy. I can weigh one if anyone is interested.
For those with 2-door saloons, these seats do NOT tilt for rear seat access.
I hope this information might be useful to others. I'll let you know how I get on trying to fit them. I might have to check the suitability of JLH's seat mounting base.
All the best for 2010
Don