I agree with Mario in that unless you are properly strapped in with a racing harness and wearing a helmet, then in the event of a crash you are much more likely to be injured by the roll bar than saved by it. Conventional seatbelts simply won't be able to locate the body securely.
For any form of motorsport, of course, it's a different matter, but for road use I would suggest a roll bar is not only unnecessary, it would be an additional avoidable risk factor.
Outside a racetrack, has anyone ever heard of or got a reference to a Morgan overturning in a road accident? I've certainly never heard of such a thing, and I've seen plenty of pictures of badly smashed-up Morgans from which the occupants survived pretty much unscathed. The Morgan in its natural state is a very safe structure to be in, without a roll bar.
