OM602 250hp/ 450ft-lb Torque.
 

What would be required to get to this level of power? I figure intercooler, the 7.5mm nozzles, Bigger turbo(which one?). propane injection?

The 7.5mm elements will have the potential to provide enough fuel for upwards of 500HP so propane is not needed. Since you're only going for 250HP, a Holset HY35 turbo will provide plenty of boost and the small turbine housing will provide a better response.

He should only have to adjust the pump a bit with the stock elements and boost it a bit more to get 250 at the crank if I am not mistaken.

Turning up the pump won't yield 250 HP and it pushes the injection duration beyond it's optimal range.

6mm elements would do it but 7 or 7.5 would work best.

what turbos will bolt up to a 602 exhaust manifold.