You are now at the perfect time to sort out the ultimate look you want from the car.
Buy the rim/tyre combo you like with the depth of dish you like etc, first.
With guards cut and flares fitted, position both wheels up in their wheel wells where you would like them to sit in regard to the flares. Now measure across from one wheel mounting face to the other. This is now the length of the diff you will need to get built.
For precision, its good to square the rims up by using a 'telescopic' axle that bolts between the 2 wheels. I made one from a couple of old axles (had to sacrifice one) some pipe and a couple of clamps. Some diff shops will loan you their workshop telescopic axle for this purpose.
For reference, you can fit 345/50/15's (approx 630 rolling dia.) under a flared hatch with a standard length diff (1440mm) and no chassis rail mods, so anything less will be a breeze.
But using std length diff measurements doesn't let you choose the exact depth of dish you like, as the rims are now dictated to by the diff length.
As for 295/15's they only seem to come in 50 series which, imho, at 675mm are way too tall aesthetically for the rear of a Torana. A better alternative (although bloody expensive) would be 285/40 series which have a rolling diameter of around 610mm.
If going 17's you could look at 235/40/17 up front and 275/35/17 rears for a pretty tough look.
Blue car in pic is not mine and obvs not a hatch but will give you an idea of what the above mentioned 17's would look like.
Red car is a mates hatch which had the 345's with std diff length.
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