All of these cars require specialist maintenance as I'm sure you're aware, but the most painless in terms of parts availability and general reliability are the V8-engined Rolls-Royce Silver Cloud and Bentley S2. These didn't arrive until the late Fifties but aside from the engine are otherwise identical to the earlier Cloud and Bentley S1 models, which are very traditional in their construction. The earlier six-cylinder models are equally delightful, but mechanical parts are harder to source.