[Power Hungry]

Honestly, the stock turbos seem to perform pretty well, especially when swapping to a 1.0 housing. Improves low RPM spool and still open enough to keep EGTs in check. My only recommendation would be to call DieselSite and order a Wicked Wheel for that turbo. Makes a noticeable improvement in airflow, particularly when pulling.

One advantage you have is that you are running a manual. EGTs are almost always caused by lugging the engine in too high of a gear. With the ability to just knock it down a gear or two and get the RPMs up, you can increase airflow through the engine which keeps the EGTs in a reasonable range. You could concieveably run a 38R turbo with a 1.0 or 1.15 housing if EGTs start getting unmanageable, but you're going to lose some bottom end as these turbos are slower to spool than the standard GTP38. I guess it all depends on the type of driving you anticipate normally operating the vehicle in.

On the Stage 1's, yes... I'm personally a big fan of keeping the nozzles stock. Unless you're spending a lot of time over 3000 RPM, stock nozzles don't have any problem discharging 160cc of fuel. On the Power Stroke counterparts, we regularly see 350-375 HP while still running the stock turbo. With appropriate exhaust (which you've already addressed), EGTs should be very manageable even as power output crests 300 HP.

The only real concern we really have on the Navistars is the rather anemic cooling system thermal dissipation. Most of these trucks run the split radiator/intercooler, and this can cause elevated operating temps at higher power outputs with heavy loads. You, however, are ahead of the game as you already addressed many of these issues with replacing the radiator (they get pretty cruddy inside) and the water pump. If your timing cover is the setup that has the coolant filter included, just make sure to change that regularly.

I hope this is helpful.