Kelvyne is very experienced, and I agree with him. If the original wheels and tyres are retained, disc brakes can be a liability. I have 5-1/2 x 13 inch wheels on my 500, fitted with 165 x 55 tyres and if I really stand on the brakes (disc at the front) I can lock them IN THE DRY! Image having that sort of braking ability in the wet with much narrower tyres---they would become dangerous. Unless one has a fairly well tuned engine which is used to it's fullest, properly set-up, the Fiat drum brakes do a perfectly adequate job.
With regard to fitting "rack and Pinion" steering----this can be quite an expensive job, and is definitely NOT a "take off one lot of parts, pop the new ones on" sort of job. A certain amount of welding (by a very competent person) is required as well that once you have cut the steering column (which you have to do) you are definitely committed! If you have a RHD car, a rack for these cars are difficult to find---I am also led to believe that, due to the layout of the pedals, a LHD car has slightly more space between the pedals, although I can't confirm this detail. Unless you are dead-set on having R 'n P steering, I would settle for an overhauled 'standard' steering box.
