I can't tell - is the car on 10's or 12's? If 12's, then is it still on the smaller 7.5" discs (or even drums maybe?) . If it is on 7.5" discs or drums and currently on 12's, then you could go to 10's without having to change the brakes - just something to bear in mind.
It's easier to get a bit of stance with 10's. I went from standard rover 12" alloys on my 1992, to 10 x 6 GB's and I think it has (for me anyway) the perfect stance. I didn't need to do anything to the bodywork, though the car already had group 2 arches. If you have standard 'special arches' you probably won't be able to go as big as 10x6 without fitting something else, like Group 2 or W&P style arches. That said, I am basing that on the assumption that you have similar rules over there regarding tyre protrusion.
If you are on 12's and plan to stay that way, then usually going up to 6" wide wheels requires some trimming of the front panel / wing. I think 5.5" is about the biggest you can go without this becoming a very likely requirement. For reference, here is a picture showing the 'stance' of my car.

Edited by spiguy, 01 May 2016 - 11:13 AM.