GD350 OM603.972 Intercooler?

Intercoolers ability to improve power output is dependent on its size - it has to be massive. Effectively there is very little in terms of power increase but fitted more to reduce thermal stress on the engine when under prolonged loads or in hotter climes.

Air temperature increases after its been churned through the turbo and with that, the air density reduces hence reduces the volumetric efficiency (in lay  terms reduces the ability to fill the cylinder).  Intercooler reduce the air temperature hence increases the air density and improve volumetric efficiency - that equates to improved power.

In order to intercool your motor involves in a lot of pipework from the turbo to intercooler to inlet manifold and find space to house the intercooler. Conventionally, these are housed infront of the coolant radiator but taking the example of the Japanese who love miniaturising things, use a small intercooler mounted on the engines rocker cover and air ducts protruding out of the bonnet. 

If you are using your vehicle for short town runs and the occasional offroading, it may not be viable to intercool. If you are in mountainous terrain and drive with heavy loads and in live in hot climate, then it could be worth your while but it is not going to be cheap.

I have a small footage that lays down principles of gauge fitting.