I'd go the intercooler. As a bonus to cooling the compressed intake air and improving the engine's efficiency, if the turbo lets go, the intercooler catches the bits before they destroy the motor.
I use to have a 308 powered fj45, It was fairly awesome, But a LS1 would be orgasmic. Seeing as your from Melb, I'll be visiting Healsville for a joy ride. What do you drink for bribes?
Jim Beam & coke in a can was the nectar of choice if I recall correctly. You'll bloody well enjoy it, I know I did and I'm pretty much hooked on diesels.
It was also great meeting another member from the forum.
have to go the exhaust mate. It would end up being less than half the price to. Duno what the intercooler kits are like for navaras but every other car ive ever turbo or intercooled using off the shelf kits always end up costing more due to unforseen issues (ie missing or unsupplied parts). Plus and intercooler is not much use if the air has got nowhere to go once it gets through your engine