Adrain

For road (and track use) 195/60 14 is a great compromise, as far as i know the original tyre was 165SR14 with a rolling diameter of approx 619.6mm, 195/60 has a rolling diameter of 589.6mm and the smaller tyre size you go the smaller the rolling diameter and the lower the gearing.
Remember the GT1600Jnr has a 4.56:1 single spinner (non LSD) Diff therefore is easy to light up the rear as it is. I have this size on my Jnr and its seems to work fine and its a popular size on lots of 105s due to the balance between grip, steering weight and rolling diameter. 185/70 was a popular size (rolling diameter 614.6mm) as its close to original but tyre choices are limited.
With rim choices 14 x 6 or 14 x 7 is the go with that tyre size and something like a GTA replica wheel which Alfaholics or classic sells in a 14 x 7 with a 24mm offset gives the car a nice tough guard filled GTA stance, clears the steering arms and does not foul the guards. If your going R spec tyres Yokie A0048s, Toyo R888 etc
thing to note is the actual tread width is wider than the size i.e 195/60 may have a tread width of 210mm
so offset is important. In the case of the minilites which are a reasonably priced they come in a range of offsets and poular sizes are again 14 x 6 and 14 x7 with you guessed it 195/60 14 tyres. Check out the alfaholics/classic alfa websites for images it gives a great insight into how your car could look and what other 105 owners are doing
Cheers
Pep