As far as engines go the rules are now pretty out there..
The maximum capacity of a replacement engine for vehicles between 800kg and 1100kg is 4x the original weight. I didn't explain that well so here is an example:
1982 1L Ute Kerb Weight - 800kg
Therefore 800 x 4 = 3200
You are allowed a 3.2L naturally aspirated engine

For turbo you times it by 2.75, so for the same vehicle you would be allowed a 2.2L turbo'd engine.
However table LA1, if you're looking, doesn't apply to 4x4's and there are no actual limitations set for these types of vehicles. Continuing from this, the weight of the vehicle is to be taken from the heaviest model of the year except for wagons. So if the ute is actually lighter than the soft top, you can take the weight of the soft top to apply your engine size.
Now you cannot have a NOS system in your car. Even if it isn't connected, it cannot be there.
Don't modify the chassis to do it, maintain the original exhaust system for that engine. The thermostat must be retained. Aftermarket computers will require emission testing.