Sadly, Rover build quality had obviously been Leylandised by the mid-1970s so watch out for badly fitted panels. These are bolted to a base unit which can rot happily, and you can’t really dismantle the car on your driveway.
Sills are structural too, and rot can easily be disguised by new outer covers. Take extreme care in checking the panels inside the rear wings (by opening the boot) as the rear suspension trailing arms are bolted to them.
Four-cylinder engines can suffer from internal corrosion of the cylinder head if anti-freeze has been neglected and water can leak from the cover plates on the blocks. Watch for overheating and excessive timing chain rattle.