Dont run low grade fuel in it without adjusting the timing!!!! The pistons are like diesels in shape, with the combustion chamber formed in the crown, and the head is flat, known as a 'Heron' head. Piston & Ring Set STD FOR Rover P6 2000 2000SC 2000TC 2.0L 4 Cylinder 1964-1972 | eBay
If low grade fuel is used and pinking occurs the sharpish edges of the valve reliefs can be eroded - I have actually seen such pistons in the 70s, not pretty.
AutoSurplus have had some interesting Rover parts lately, worth perusing.
I would have thought the US would have represented only a relatively small number of those LHD sales. It was a very expensive car there and despite the rave reviews probably only had a limited customer base (it was pretty small for starters). I'm in Switzerland and I'm guessing outside the UK, per capita we'd have the most cars still on the road. I've seen probably around 40-50 in the last decades and more turn up all the time. Quite a lot of cars in the rest of Europe seem to originate here too as they tend to survive in relatively good condition.