I'd be a whole lot more concerned with the steering effort needed putting substantially wider tires on an 1800. A Falcon (I had a 1960 in the distant past) has such slow steering the mechanical advantage could overcome a bigger footprint - but an 1800 without power steering - it may be quite uncomfortable.
Volvo 1800, 122, and 140 models are sometimes mocked for having so many turns lock to lock but the ratio is not as slow as the number of turns may indicate - those models have a relatively small turning circle--the wheels can turn more than most. I think if the limit was more like other cars the lock to lock would be more like 3 turns rather than the 4+ they have. - Dave