How much offset you can run depends on the wheel width and the tire size.

The stock offset is +30 mm with 4" wide wheels. Most 5.5" wide wheels with appropriate offset will fit under the fenders of a Datsun 1200. Most 6-inch wide will not fit inside the gaurds, but theoretically (with the right offset) it is possible. Utes can fit wider wheels on the rear.

Tires: if you have 13" low profile you can run any amount of positive offset, like these 9-inch wide watanabes: