Well no, of course the big axles are stronger. But then stronger is all relative and it depends on the amount of abuse you intend giving it. Disc brake rear ends are pretty pricey and you are unlikely to know whether it is a small or large axle unit till you pull the centre out. As mentioned, the large axles are very hard to find and the tercel ones are not a direct replacement. Of course the centre you get needs to match the axles in size. These large axle T series rear ends are only found in late AE86's never delivered in Australia.
If you are concerned, you can always spend the money on the hiace conversion at the added cost of extra weight.
Otherwise you could bolt in a T18 rear end which will be fine for width (don't forget to factor this into your thinking), and axles are available fairly easily, plus a T series LSD will bolt in.